Slipcover

Changes in this release:
- fixed file filter not being used for modules loaded through `pytest`, including uninteresting coverage results;
- simplified statistics gathering, also greatly improving its performance;

An error in the build scripts was causing non-x86_64 code to be dropped.

Changes in release:
- fixed `pytest` plugins not being loaded, due to a conflict between how Slipcover was manipulating `sys.meta_path` and `importlib.metadata`'s package detection. Note that some plugins may not yet work (notably, `pytest-xdist`) -- see 9.
- added handler for `MetaPathFinder`s that don't implement `find_spec`;

Changes in this release:
- Fixed tracker module not always loading with Python 3.8 on Windows, due to Microsoft Studio dependencies;
- Fixed description links on pypi;
- Improved Python library path detection (still needs work, though);
- Fixed missing wheels for Python 3.9 and 3.10;

This release fixes https://github.com/plasma-umass/slipcover/issues/4 from v0.1.1, which happens with pytest isn't installed.

Changes:
- Slipcover now interposes on pytest, so that you can get coverage results on those files as well;
- Fixed function finder not finding static and class methods (affected performance, not correctness);