Merge pull request #13 from kpartlow/master

Added in tests for null cases, IllegalStateExceptions, and hard to hit c...
- added support for 'Default Column' on Rule Axes.  When no conditions fire, and there is a default column, then it will fire (be treated like it is 'true') and the associated cell will be executed.  This works with any number of rule axes on a given n-cube.
Added tests in for exception cases and parser errors, refactored duplicate code, removed unused code.
Made Proximity (static only class) final.  Removed usage where Column was checking for Instancof Proximity.  Added in tests for Proximity Exception Case