Removing pycurl and tox, and setting up new testing suite

This release removes the pycurl dependency and the associated code, as well as tox and the old tests. I've started a new test setup and will be building out those tests soon, but for right now, these tests exist in a very early state.

After installing requirements-dev.txt, you can run the tests with make!

Also included are some more type annotations, and some expanded docstrings in certain functions/methods.