allow greek symbols in identifiers

com.oracle.truffle.r.parser/src/com/oracle/truffle/r/parser/ParserGeneration.java

@@ -93,6 +93,7 @@ public class ParserGeneration {
         "support for file delimiter",
         "pass along TruffleRLanguage",
         "convert line endings",
-        "handle four and more dots as identifier"
+        "handle four and more dots as identifier",
+        "allow greek characters in identifiers"
     };
 }

com.oracle.truffle.r.parser/src/com/oracle/truffle/r/parser/R.g

@@ -767,7 +767,7 @@ fragment OP_NAME
     | ('*'|'/'|'+'|'-'|'>'|'<'|'='|'|'|'&'|':'|'^'|'.'|'~'|','|'?')
     ;
 
-fragment ID_NAME : ('a'..'z'|'A'..'Z'|'_') ('a'..'z'|'A'..'Z'|'0'..'9'|'_'|'.')* ;
+fragment ID_NAME : ('a'..'z'|'A'..'Z'|'α'..'ω'|'Α'..'Ω'|'_') ('a'..'z'|'A'..'Z'|'0'..'9'|'α'..'ω'|'Α'..'Ω'|'_'|'.')* ;
 
 fragment ESC_SEQ
     : '\\' ('b'|'t'|'n'|'f'|'r'|'"'|'\''|'`'|'\\'|' '|'a'|'v')