Replace hand-coded lexer with faster hacky lexer.

lib/liquid/parser.rb

@@ -3,8 +3,12 @@ module Liquid
   # it provides helpers and encapsulates state
   class Parser
     def initialize(input)
-      @input = input
+      @tokens = tokenize(input)
       @p = 0 # pointer to current location
     end
+
+    def tokenize(input)
+      input.split(/\b/).map {|tok| tok.strip}
+    end
   end
 end