Project restructure and OSX posix implementation

- Restructured the project to partition the header files into logical
  groups. This was done primarily to stop the header naming conflict
  between syscommon's Semaphore.h and the native posix semaphore.h
- Added ant build system (based on the Portico build system)
- Added Platform implementation for OSX/Posix. Need to test this on a
  linux box to iron out any discrepancies in behavior.
- Added some remedial unit tests
- Added the Event class for inter-thread signaling