Belarusian: fix IPA chars

- fix IPA chars for "s;" and "z;" phonemes
- add bug note about "...i a..." case

dictsource/be_rules

        з (L06L04 z;
        з (ці   s;
 
-.group і
+.group і       // NOTE: appends ";" at the end of the words when next starts from "а"
        і       i
     C) і       ;i
 

phsource/ph_belarusian

   FMT(r3/r_trill2) addWav(r3/r_trill2.wav, 65)
 endphoneme
 
+phoneme s;
+  import_phoneme base1/s;
+  ipa sʲ
+endphoneme
+
+phoneme z;
+  import_phoneme base1/z;
+  ipa zʲ
+endphoneme
+
 phoneme ;
   liquid pzd
   lengthmod 0