Graphics 2.0 Fix

Corona SDK recently upgraded their graphics library to their '2.0' library.  With this change several things were deprecated or removed.  As such the Chartboost plugin ceased to work properly with the new 2.0 library.

Working sample:
  * Running the Chartboost plugin with Corona SDK build numbers lower than 2013.2000 and it will run the plugin as is.
  * When the plugin is run (without this pull request) with any builds over 2013.2000 (which utilizes the Graphics 2.0 library) will cause errors as alerted in several issues on the repo.
  * This pull request can be tested with a build over 2013.2000 (built using build 2013.2100) and the plugin will now work with the Graphics 2.0 library.  No other functionality was added. 

Changes:
  Changes are documented in the CHANGELOG.md file in this pull request.  Most changes were minor and involved positioning, color, and sizes with several functions that changed.  

Fixes:
 This pull request fixes #8 and also fixes #9

Please let me know if more info is needed on my part.