docs: Document the lexical set transcriptions used by the en language files.

docs/languages/gmw/en.md

 by comparing the Received Pronunciation British (RP) and General American
 (GenAm) accents in use at that time.
 
+The `en` transcriptions listed below are the phonemes used by eSpeak NG to
+transcribe the different lexical sets.
+
 ## Short Vowels
 
-| Lexical Set | RP    | GenAm |
-|-------------|-------|-------|
-| KIT         | ɪ     | ɪ     |
-| DRESS       | e     | ɛ     |
-| TRAP        | æ     | æ     |
-| LOT         | ɒ     | ɑ     |
-| STRUT       | ʌ     | ʌ     |
-| FOOT        | ʊ     | ʊ     |
+| Lexical Set | en    | RP    | GenAm |
+|-------------|-------|-------|-------|
+| KIT         | `I`   | ɪ     | ɪ     |
+| DRESS       | `E`   | e     | ɛ     |
+| TRAP        | `a`   | æ     | æ     |
+| LOT         | `0`   | ɒ     | ɑ     |
+| STRUT       | `V`   | ʌ     | ʌ     |
+| FOOT        | `U`   | ʊ     | ʊ     |
 
 ## Long Vowels
 
-| Lexical Set | RP    | GenAm |
-|-------------|-------|-------|
-| FLEECE      | iː    | i     |
-| PALM        | ɑː    | ɑ     |
-| THOUGHT     | ɔː    | ɔ     |
-| GOOSE       | uː    | u     |
+| Lexical Set | en    | RP    | GenAm |
+|-------------|-------|-------|-------|
+| FLEECE      | `i:`  | iː    | i     |
+| PALM        | `A:`  | ɑː    | ɑ     |
+| THOUGHT     | `O:`  | ɔː    | ɔ     |
+| GOOSE       | `u:`  | uː    | u     |
 
 ## Rhotic Vowels
 
 These are vowels that are followed by an `r` that is not part of the next syllable
 when considering the root form of the word containing that vowel.
 
-| Lexical Set | RP    | GenAm |
-|-------------|-------|-------|
-| NURSE       | ɜː    | ɝ     |
-| START       | ɑː    | ɑɹ    |
-| NORTH       | ɔː    | ɔɹ    |
-| FORCE       | ɔː    | oɹ    |
-| CURE        | ʊə̯     | ʊɹ    |
-| NEAR        | ɪə̯     | ɪɹ    |
-| SQUARE      | eə̯     | ɛɹ    |
+| Lexical Set | en    | RP    | GenAm |
+|-------------|-------|-------|-------|
+| NURSE       | `3:`  | ɜː    | ɝ     |
+| START       | `A@`  | ɑː    | ɑɹ    |
+| NORTH       | `O@`  | ɔː    | ɔɹ    |
+| FORCE       | `o@`  | ɔː    | oɹ    |
+| CURE        | `U@`  | ʊə̯     | ʊɹ    |
+| NEAR        | `i@3` | ɪə̯     | ɪɹ    |
+| SQUARE      | `e@`  | eə̯     | ɛɹ    |
+
+__NOTE:__ `/i@3/` is used for the NEAR lexical set to differentiate it from
+`/i@/` used in words like `million`.
 
 ## Reduced Vowels
 
 These are unstressed vowels that differ from the vowels in the main lexical sets.
 
-| Lexical Set | RP    | GenAm |
-|-------------|-------|-------|
-| HAPPY       | ɪ     | i     |
-| COMMA       | ə     | ə     |
-| LETTER      | ə     | ɚ     |
+| Lexical Set | en    | RP    | GenAm |
+|-------------|-------|-------|-------|
+| HAPPY       | `i`   | ɪ     | i     |
+| COMMA       | `@`   | ə     | ə     |
+| LETTER      | `3`   | ə     | ɚ     |
 
 ## Diphthongs
 
-| Lexical Set | RP    | GenAm |
-|-------------|-------|-------|
-| FACE        | eɪ̯     | eɪ̯     |
-| PRICE       | aɪ̯     | aɪ̯     |
-| CHOICE      | ɔɪ̯     | ɔɪ̯     |
-| GOAT        | əʊ̯     | oʊ̯     |
-| MOUTH       | aʊ̯     | aʊ̯     |
+| Lexical Set | en    | RP    | GenAm |
+|-------------|-------|-------|-------|
+| FACE        | `eI`  | eɪ̯     | eɪ̯     |
+| PRICE       | `aI`  | aɪ̯     | aɪ̯     |
+| CHOICE      | `OI`  | ɔɪ̯     | ɔɪ̯     |
+| GOAT        | `oU`  | əʊ̯     | oʊ̯     |
+| MOUTH       | `aU`  | aʊ̯     | aʊ̯     |
 
 ## Split Vowels
 
 sets in both RP and GenAm, so have split from one of those lexical sets and
 merged with the other.
 
-| Lexical Set | RP    | GenAm |
-|-------------|-------|-------|
-| BATH        | ɑː    | æ     |
-| CLOTH       | ɒ     | ɔ     |
+| Lexical Set | en    | RP    | GenAm |
+|-------------|-------|-------|-------|
+| BATH        | `aa`  | ɑː    | æ     |
+| CLOTH       | `0`   | ɒ     | ɔ     |
+
+__NOTE:__ eSpeak NG does not have a distinct transcription for the CLOTH lexical
+set. As such, it can only represent American English accents with the COT-CAUGHT
+merger where COT is the American PALM-LOT merger and CAUGHT is the American
+THOUGHT-CLOTH merger.
 
 ## References
 

phsource/ph_english

 // VOWELS
 //*******************************************************************
 
-phoneme @    //  Schwa
+phoneme @
   vwl   starttype #@  endtype #@
   unstressed
   length 140
 endphoneme
 
 
-phoneme 3    //  Schwa, used for rhotic schwa in American, e.g. bett**er**
+phoneme 3
   CALL @
   ipa ə
 endphoneme
 endphoneme
 
 
-phoneme aa   //   'b**a**th' etc. This is \[a\] in some accents, \[A:\] in others.
+phoneme aa
   vwl  starttype #a  endtype #a
   ipa a
   length 200
 endphoneme
 
 
-phoneme E // dr**e**ss
+phoneme E
   vwl  starttype #e  endtype #e
   length 140
   IF nextPhW(n) THEN
 
 
 
-phoneme I // k**i**t
+phoneme I
   vwl  starttype #i  endtype #i
   length 130
   IfNextVowelAppend(;)
 endphoneme
 
 
-phoneme i   // happ**y**. optional variant of [I] for end of words
+phoneme i
   vwl  starttype #i  endtype #i
   unstressed
   ipa i
 endphoneme
 
 
-phoneme 0 // l**o**t
+phoneme 0
   vwl  starttype #o  endtype #o
   length 140
   ChangeIfDiminished(@)
 endphoneme
 
 
-phoneme V // str**u**t
+phoneme V
   vwl  starttype #a  endtype #@
   length 140
 
 endphoneme
 
 
-phoneme U // f**oo**t
+phoneme U
   vwl  starttype #o  endtype #o
   length 150
   
 
 
 
-phoneme A: // p**al**m
+phoneme A:
   vwl  starttype #a  endtype #a
   length 230
   IfNextVowelAppend(r-)
 endphoneme
 
 
-phoneme A@     // st**ar**t. Used for [A:] when followed by 'r'.
+phoneme A@
   vwl  starttype #a  endtype #a
   ipa ɑː
   length 230
 
 
 
-phoneme 3: // n**ur**se
+phoneme 3:
   vwl  starttype #@  endtype #@
   length 210
   IfNextVowelAppend(r-)
 endphoneme
 
 
-phoneme i: // fl**ee**ce
+phoneme i:
   vwl  starttype #i  endtype #i
   length 175
   IfNextVowelAppend(;)
 endphoneme
 
 
-phoneme O: // th**ou**ght
+phoneme O:
   vwl  starttype #o  endtype #o
   length 230
   ChangeIfDiminished(@)
 endphoneme
 
 
-phoneme O@ // n**or**th
+phoneme O@
   vwl  starttype #o  endtype #o
   ipa ɔː
   length 240
 endphoneme
 
 
-phoneme o@ // f**or**ce
+phoneme o@
   vwl  starttype #o  endtype #o
   ipa ɔː
   length 250
 endphoneme
 
 
-phoneme u: // g**oo**se
+phoneme u:
   vwl  starttype #u  endtype #u
   length 210
   IF nextPh(l/2) THEN
 endphoneme
 
 
-phoneme aU // m**ou**th
+phoneme aU
   vwl  starttype #a  endtype #u
   length 230
   FMT(vdiph/au)
 endphoneme
 
 
-phoneme oU // g**oa**t
+phoneme oU
   vwl  starttype #@  endtype #u
   ipa əʊ
   length 220
 endphoneme
 
 
-phoneme aI // pr**i**ce
+phoneme aI
   vwl  starttype #a  endtype #i
   length 240
   IF nextPh(#a) THEN
 endphoneme
 
 
-phoneme eI // f**a**ce
+phoneme eI
   vwl  starttype #e  endtype #i
   length 210
   FMT(vdiph/eei)
 endphoneme
 
 
-phoneme OI // ch**oi**ce
+phoneme OI
   vwl  starttype #o  endtype #i
   length 230
   FMT(vdiph/ooi)
 endphoneme
 
 
-phoneme e@ // squ**are**
+phoneme e@
   vwl  starttype #e  endtype #@
   length 230
   IfNextVowelAppend(r-)
 endphoneme
 
 
-phoneme i@ // mill**io**n
+phoneme i@
   vwl  starttype #i  endtype #@
   length 250
   IfNextVowelAppend(r-)
 endphoneme
 
 
-phoneme i@3 // n**ear**
+phoneme i@3
   vwl  starttype #i  endtype #@
   length 250
   
 endphoneme
 
 
-phoneme U@ // c**ure**
+phoneme U@
   vwl  starttype #u  endtype #@
   length 200
   IfNextVowelAppend(r-)