Add '.' and ':' to the set of allowable operator symbols.

This fixes part of #368.

src/Cryptol/Parser/Lexer.x

@@ -39,7 +39,7 @@ $unitick        = \x7
 @id_next      = [a-zA-Z0-9_'] | $unilower | $uniupper | $unidigit | $unitick
 
 @id           = @id_first @id_next*
-@op           = ([\!\@\#\$\%\^\&\*\~\>\<\?\+\=\|\/\\\-] | $unisymbol)+
+@op           = ([\!\#\$\%\&\*\+\-\.\/\:\<\=\>\?\@\\\^\|\~] | $unisymbol)+
 
 @qual         = (@id $white* :: $white*)+
 @qual_id      = @qual @id