Belarusian: fix IPA chars (#1572)

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

dictsource/be_rules

@@ -80,7 +80,7 @@
        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

@@ -72,6 +72,16 @@ phoneme r
   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