Document the Kirshenbaum IPA features.

docs/phoneme_features.md

+# Phoneme Features
+
+- [Phoneme Type](#phoneme-type)
+- [Consonants](#consonants)
+  - [Voicing](#voicing)
+  - [Place of Articulation](#place-of-articulation)
+  - [Manner of Articulation](#manner-of-articulation)
+- [Vowels](#vowels)
+  - [Height](#height)
+  - [Backness](#backness)
+  - [Rounding](#rounding)
+- [Additional Features](#additional-features)
+- [References](#references)
+
+----------
+
+Evan Kirshenbaum created an ASCII transcription of the International Phonetic
+Alphabet<sup> \[<a href="#ref1">1</a>\]</sup>. As well as using ASCII
+characters for specific IPA phonemes, this transcription provides a set of
+3-letter feature abbreviations allowing a phoneme to be described as a sequence
+of features.
+
+This document describes the features used by Kirshenbaum.
+
+## Phoneme Type
+
+| Feature | Name            |
+|---------|-----------------|
+| `vwl`   | vowel           |
+
+## Consonants
+
+### Voicing
+
+| Feature | Name            |
+|---------|-----------------|
+| `vcd`   | voiced          |
+| `vls`   | voiceless       |
+
+### Place of Articulation
+
+| Feature | Name            |
+|---------|-----------------|
+| `blb`   | bilabial        |
+| `lbd`   | labio-dental    |
+| `dnt`   | dental          |
+| `alv`   | alveolar        |
+| `rfx`   | retroflex       |
+| `pla`   | palato-alveolar |
+| `pal`   | palatal         |
+| `vel`   | velar           |
+| `lbv`   | labio-velar     |
+| `uvl`   | uvular          |
+| `phr`   | pharyngeal      |
+| `glt`   | glottal         |
+
+### Manner of Articulation
+
+| Feature | Name            |
+|---------|-----------------|
+| `stp`   | stop            |
+| `frc`   | fricative       |
+| `nas`   | nasal           |
+| `orl`   | oral            |
+| `apr`   | approximant     |
+| `lat`   | lateral         |
+| `ctl`   | central         |
+| `trl`   | trill           |
+| `flp`   | tap/flap        |
+| `clk`   | click           |
+| `ejc`   | ejective        |
+| `imp`   | implosive       |
+
+## Vowels
+
+### Height
+
+| Feature | Name            |
+|---------|-----------------|
+| `hgh`   | high            |
+| `smh`   | semi-high       |
+| `umd`   | upper-mid       |
+| `mid`   | mid             |
+| `lmd`   | lower-mid       |
+| `low`   | low             |
+
+### Backness
+
+| Feature | Name            |
+|---------|-----------------|
+| `fnt`   | front           |
+| `cnt`   | center          |
+| `bck`   | back            |
+
+### Rounding
+
+| Feature | Name            |
+|---------|-----------------|
+| `unr`   | unrounded       |
+| `rnd`   | rounded         |
+
+## Additional Features
+
+| Feature | Name            |
+|---------|-----------------|
+| `asp`   | aspirated       |
+| `unx`   | unexploded      |
+| `syl`   | syllabic        |
+| `mrm`   | murmured        |
+| `lng`   | long            |
+| `vzd`   | velarized       |
+| `lzd`   | labialized      |
+| `pzd`   | palatalized     |
+| `rzd`   | rhoticized      |
+| `nzd`   | nasalized       |
+| `fzd`   | pharyngealized  |
+
+## References
+
+1. <a name="ref1"></a> Kirshenbaum, Evan,
+   [http://www.kirshenbaum.net/IPA/ascii-ipa.pdf](Representing IPA phonetics in ASCII). 2001.