Support quoted symbol for JSON-style hash literal

Like below:

{ 'first': 1, "second": 2 }

Author: aycabta

lib/rdoc/ruby_lex.rb

@@ -112,6 +112,7 @@ def initialize(content, options)
     @indent_stack = []
     @lex_state = :EXPR_BEG
     @space_seen = false
+    @after_question = false
 
     @continue = false
     @line = ""
@@ -379,6 +380,8 @@ def token
         tk = tk1
       end
     end
+    @after_question = false if @after_question and !(TkQUESTION === tk)
+
     #      Tracer.off
     tk
   end
@@ -593,6 +596,7 @@ def lex_init()
       |op, io|
       if @lex_state == :EXPR_END
         @lex_state = :EXPR_BEG
+        @after_question = true
         Token(TkQUESTION)
       else
         ch = getc
@@ -1359,7 +1363,10 @@ def identify_string(ltype, quoted = ltype, type = nil)
         end
       end
 
-      if subtype
+      if peek(0) == ':' and !peek_match?(/^::/) and :EXPR_BEG == @lex_state and !@after_question
+        str.concat getc
+        return Token(TkSYMBOL, str)
+      elsif subtype
         Token(DLtype2Token[ltype], str)
       else
         Token(Ltype2Token[ltype], str)