tr: add pronunciation rules for vowels â, ô, û.

Related to #500.

dictsource/tr_rules

 
 .group a
         a        a
-
      @) a (_S1   a
 
      @) acak (_S4  adZak
 
      @) avru (pa avr'u
 
+.group â
+	â	 a
+
+
 .group b
         b        b
         bb       _:_!b   // Doubled voiceless consonants
 .group ö
         ö        W
 
+.group ô
+	ô	o
+
 .group p
         p        p
         pp       _:_!p
      @) ün (_S2  yn
 
 
+
+.group û
+	û	u  
+
 .group v
         v        v