Portalocker

* Added msvcrt support for Windows

* Python 3 support

* Fixing a few bugs, added coveralls support, switched to py.test and added
100% test coverage.

- Fixing exception thrown when fail_when_locked is true
- Fixing exception "Lock object has no attribute '_release_lock'" when
fail_when_locked is true due to the call to Lock._release_lock() which
fails because _release_lock is not defined.

* Now actually returning the file descriptor from the `Lock` class

* Added `Lock` class to help prevent cache race conditions

* Initial release