Feature/add typechecking

[techalchemy]

• Massive performance gains
• Type checking
• Regression test for shims being removed
• Add typehint coverate to full library
• Update tox config
• Fix shim removal to only remove shims under the same conditions as we
  would activate the finders in question
• Better regexes
• Regresses 2.7.15+ version parsing atm

[techalchemy]

The sheer number of bugs this caught is actually crazy.

[techalchemy]

hrm i've been struggling with caching / clearing the cache... on here...

[jxltom]

Check the CI, the result is very interesting. It looks like it is not problem with xdist. The tests are still failing in python34 and 35

[jxltom]

Finally I figured out why the tests are failing. It is because PythonVersion.from_path is trying to parse from name and then from absolute path (if former one fails). In some cases, such as python35 in Travis, the name is 3.5 and PythonVersion.parse will successfully parse it though patch will be None in this case. I think it is better to parse from path (via calling subprocess) and then from name, which can get as more info as possible.

Feel free to revert this commit if you don't like it. 😃

[techalchemy]

No we definitely want to avoid that. We just need to handle name correctly.

I swapped them because I profiled with a flamegraph and subprocess calls are wildly slow. Swapping the ordering here cut the runtime in 1/9. It should just use subprocess if it thinks it has a python version but actually doesn’t t

[jxltom]

Oh, it is for the performance. I missed that. So we only need to handle the names better.

I reverted the commit :D

[techalchemy]

I didn't indicate it anywhere :p I just benchmarked locally