Finished the algorithm for checking the words. We now make sure the word isn't too...

Finished the algorithm for checking the words. We now make sure the word isn't too long, does not contain other characters, and the occurrence of the characters in the word is less than or equal to the number in the tile string

* Source/NSStringAdditions.h:
* Source/NSStringAdditions.m:
([NSString(NSStringAdditions) occurenceOfChar:]): New Method
* Scrabbalize.xcodeproj: Project changes for NSStringAdditions
* Source/AppController.m: Use the new algorithm and occurence method