Write tests

[nilsnolde]

After #6 and #7, we can focus on writing some tests. I'd keep it fairly simple and basically only test that the bindings themselves work, i.e. calling each function and making sure the basic objects exist in the response. We can just use unittest for this, e.g. like here: https://github.com/gis-ops/pyvalhalla/blob/master/test/test_utrecht.py. We'll also want to test any abstractions we add in #7

[nilsnolde]

this has landed with #9