TravisCI: Test with Python 3.3 too
setup.py: Disable shapely dependency on Python 3.0 and above
test_shape: Skip tests if the shapely import fails

This will skip the shapely-related tests on Python 3
test_elements: Explicitly pass byte strings to WKBElement
Merge pull request #21 from Turbo87/py3.3

Added Python 3.3 support for TravisCI