Allow Recursive Transliteration from a Transliteration Callback.

[sayak-sarkar]

'[a-z][0-9]', function(input){
return tras($1+trans($2));
}

Required for porting bn-disha to jquery.ime, wherein there is a requirement to make a recursive callback to the transliterate method to for a range of characters.

Example:-
For a range of consonants inputs, the following result is required:-

['ি([b-d])', 'i', trans($1)ি}],