Python 3.11 wheels, experimental option, source distribution fixes

This release:

• fixes failing tests with Python 3.11;
• adds wheels for Python 3.11;
• adds an experimental option, --immediate, which essentially implements on-stack replacement by ignoring Python's rule that code objects should be immutable. Using it further reduces overhead, as Slipcover need not generate new code objects or update references to it. Use at your own risk... this is really only intended for research purposes;
• fixes an include file, ironically, not being included into the source distribution;

Bugfix release

This release:

• fixes a bug causing Slipcover to move functions' docstrings when doing branch coverage, so that they could no longer be found;
• advances version to 0.2.0 given the support for branch coverage;

Branch coverage support, per-file and global summaries

This release:

• adds branch coverage measuring support to slipcover; simply run it with --branch to get it.
• adds a "meta" item identify the source of the coverage information, as well as per-file and global summaries to the JSON output (issue #2).

Packaging tweak

This release:

• fixes a packaging issue omitting Python 3.11 from classifiers;
• acknowledges pypy support, contributed by @cfbolz, and actually added in v0.1.7;

Python 3.11 support

This release:

• adds support for Python 3.11 (technically 3.11.0b3);
• changes missing lines text formatting to include any non-code lines between missing ones, simplifying output and aligning it with Coverage.py;

Fixing file filtering

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;

Fixes missing Apple Silicon (M1) code in wheels

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

Fixed pytest plugins not being loaded

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 MetaPathFinders that don't implement find_spec;

Bugfix release: tracker loading on Windows

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;

Fixing pytest import issue from v0.1.1

This release fixes #4 from v0.1.1, which happens with pytest isn't installed.