Separate ? and - into special tokens

lib/liquid/lexer.rb

@@ -9,9 +9,11 @@ module Liquid
       '['.freeze => :open_square,
       ']'.freeze => :close_square,
       '('.freeze => :open_round,
-      ')'.freeze => :close_round
+      ')'.freeze => :close_round,
+      '?'.freeze => :question,
+      '-'.freeze => :dash
     }
-    IDENTIFIER = /[\w\-?!]+/
+    IDENTIFIER = /\w+/
     SINGLE_STRING_LITERAL = /'[^\']*'/
     DOUBLE_STRING_LITERAL = /"[^\"]*"/
     NUMBER_LITERAL = /-?\d+(\.\d+)?/

lib/liquid/parser.rb

@@ -75,6 +75,13 @@ module Liquid
 
     def variable_signature
       str = consume(:id)
+      while consume?(:dash)
+        str << "-".freeze
+        str << consume(:id) if look(:id)
+      end
+      if consume?(:question)
+        str << "?".freeze
+      end
       if look(:open_square)
         str << consume
         str << expression