Remove CPU overheads in _query_disc.pyx.

1. The isnsideok call could take up to 50% of the CPU time for a typical query_* call. Resolved.
2. Allow passing in of a buffer to remove overhead of reallocating memory when repeated query_* calls are made.
3. Switch off bounds checking in pixset_to_array
Remove trailing whitespace
Change RuntimeError to ValueError for consistency with behaviour e.g. of numpy ufuncs. Add unit test for buffer-mode query_disc
Use assertRaises instead of catching exception
Further style changes
Merge pull request #184 from apontzen/master

Improve _query_disc.pyx.