* support 3d model filtering
* fix lint error: blank line contains whitespace
* add model extensions to test runner mimetype cache manually
* use unittest.mock.patch
* remove mtl file from testcase (actually plaintext support file)
* Run unit tests on Windows as well.
* Test on mac.
* Continue running on error.
* Compared normalized paths to work cross platform.
* Only test common set of mimetypes across operating systems.