Remove dependency on activesupport for camelize

Progress toward sferik#264.

lib/twitter/action_factory.rb

@@ -1,13 +1,14 @@
-require 'active_support/core_ext/string/inflections'
 require 'twitter/favorite'
 require 'twitter/follow'
+require 'twitter/inflector'
 require 'twitter/list_member_added'
 require 'twitter/mention'
 require 'twitter/reply'
 require 'twitter/retweet'
 
 module Twitter
   class ActionFactory
+    extend Twitter::Inflector
 
     # Instantiates a new action object
     #
@@ -17,7 +18,7 @@ class ActionFactory
     def self.new(action={})
       type = action.delete('action')
       if type
-        Twitter.const_get(type.camelize.to_sym).new(action)
+        Twitter.const_get(camelize(type).to_sym).new(action)
       else
         raise ArgumentError, "argument must have an 'action' key"
       end

lib/twitter/inflector.rb

@@ -0,0 +1,13 @@
+module Twitter
+  module Inflector
+
+    # Converts a snake_case string to CamelCase
+    #
+    # @params string [String]
+    # @return [String]
+    def camelize(string)
+      string.split('_').map(&:capitalize).join
+    end
+
+  end
+end