Install packages from requirements-dev.txt.
TST: Use ubuntugis repo to install newer GEOS on Travis CI
Address @olt's comments on #63.

Change to _reader and _writer, remove module readers and writers in
favor of ones local to methods. Fixes #63. New issues for all future
WK* reader/writer bugs and features, please :)
Expand related fixes mentioned in #74 for EMPTY geometries
 - ops.transform now returns geometries that are empty, similar to fix for
   affine_transform; formerly this raised an exception:
   "AttributeError: 'Point' object has no attribute 'geoms'"
 - Add test cases for transform and affine_transform
 - Further PEP8 to affinity.py, ops.py