Initial refactoring of webcl-validator to libclv library with public C API, and a driver binary using it

This allows using the validator e.g. in a browser at a basic level. The public C API and open questions are described in Issue #51.

Relatedly, it was decided to change the types in the JSON header from C runtime host types to OpenCL C types and one test was changed to reflect this.

Otherwise, the existing tests for webcl-validator pass with the refactored version at least on Win32+VS2012. Testing on other platforms welcome.

Still TODO:
- error reporting is limited to "were there errors" in current API, the library prints the actual errors/warnings straight to console; need to decide the granularity of the API first (estimate 2d)
- async validation, currently clvValidate just ignores the callback argument (estimate 1d for win32 + pthread)
- selectively unit testing the library directly in addition to the webcl-validator test suite, if coverage is otherwise insufficient (estimate 2d)
- API documentation, currently just header comments (later?)
- library is static until API is settled (very easy to change)