Misc fixes

[skirpichev]

• use pythoncapi-compat's pythoncapi_compat.h
• use _PyLong_Sign() instead of _PyLong_IsNegative()
• removed build-wheels.conf // seems to be unused
• reuse mpz_set_PyLong in GMPy_MPZ_From_PyLong() and GMPy_XMPZ_From_PyLong()
• fix install.rst (move up "From Sources" section)
• move changelogs for 1.x versions from gmpy2.c to history.rst
• move changelogs for 2.0.0b1 from gmpy2.c to history.rst
• move changelogs for 2.0.0b[234] from gmpy2.c to history.rst
• move changelogs for 2.0.0 and 2.1.x from gmpy2.c to history.rst
• update changelog for 2.2.0 (from gmpy2.c), closes #329

[codecov-commenter]

Codecov Report

Attention: Patch coverage is 89.47368% with 4 lines in your changes are missing coverage. Please review.

Project coverage is 85.52%. Comparing base (eb8dfcb) to head (283c665). Report is 7 commits behind head on master.

Files	Patch %	Lines
src/gmpy2_cache.c	50.00%	4 Missing :warning:

:exclamation: Your organization needs to install the Codecov GitHub app to enable full functionality.

Additional details and impacted files

```diff @@ Coverage Diff @@ ## master #471 +/- ## ========================================== - Coverage 85.55% 85.52% -0.03% ========================================== Files 49 50 +1 Lines 11678 11656 -22 Branches 2209 2202 -7 ========================================== - Hits 9991 9969 -22 Misses 1687 1687 ```

:umbrella: View full report in Codecov by Sentry.
:loudspeaker: Have feedback on the report? Share it here.

[casevh]

Looks good. Thanks for all the cleanup.

casevh