* Added get_context to Variables
* Added support for interfacing MADARA containers to Variables as well as Knowledge_Base
* Added exchange method to Integer, String, and Map
  * Allows exchanging variable values between logical offsets in a context
* Updated version to 1.5.7

git-svn-id: http://madara.googlecode.com/svn/trunk@1239 2850746a-f1c8-11dd-b507-8b4ecd5210be