Modified vectorized contains function to accept 1D point arrays.

Per the discussion on PR #118, referenced in #119 and originally
proposed in #116, the vectorized contains function has been modified to
support .xy attribute inputs.
ENH: Cleanup of vectorized contains code, performance enhancements.

I removed the 2-dimensional version of `contains` and the new tests
reflect this change as well.
FIX: Added _geos.pxi to MANIFEST.in so source distributions have the file.
Refactored the cython code and released the gil.