Update Windows builds for PHP 8.0

[AlexNDRmac]

Hello!

• Type: CI | Builds

Small description of change:

• Added ability to compile extensions Witt Visual Studio 2019
• Added PHP 8 to matrix builds
• Updated readme

Thanks

[codecov]

Codecov Report

Merging #100 (60e6e53) into master (c703f67) will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##           master     #100   +/-   ##
=======================================
  Coverage   75.09%   75.09%           
=======================================
  Files           5        5           
  Lines        2891     2891           
=======================================
  Hits         2171     2171           
  Misses        720      720           

Flag	Coverage Δ
unittests	75.09% <ø> (ø)

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