Added stubtractor class.
operator overloads for subtractor.
Subtractor generator.
Copied over xcode project from master to get tests working.
Merge branch 'master' into MP-Operator-Work
* Added tests for operators.
* Fixed some errors caught by tests
* Added operators for Generator / ControlGenerator combinations.
ControlDivider class.
Multipliers now work with audio/control rate combinations.
Divider tested and working.
Divide by zero handling.
Merge pull request #132 from TonicAudio/MP-Operator-Work

Subtract and Divide operators
Merge from master