Cleanup of failing tests on windows and imports in _features.pyx

This pull requests cleans up 2 sets of tests that were failing on windows, and migrated tests in tests/test_write.py to use py.test.  The tests were failing due to platform specific decimal precision and line ending issues.

This pull request also cleans up imports used in _features.pyx, including switching from the duplicate code for io_ubyte() which was already defined in _io.pyx.