Add CI using Github Actions

[marcinlos]

Simple CI pipeline using Github Actions. Closes #9

Features:

• Builds using GCC 7-11 and Clang 6, 10, 12
• Configuration w/ and w/o Galois and MUMPS
• Run with Address and UB sanitizers
• Code coverage using Codecov
• Formatting check using clang-format
• Spellcheck using codespell
• Header guards and copyright lines check

[codecov[bot]]

Codecov Report

:exclamation: No coverage uploaded for pull request base (develop@0ef4f99). Click here to learn what that means. The diff coverage is n/a.

@@            Coverage Diff             @@
##             develop      #47   +/-   ##
==========================================
  Coverage           ?   23.64%           
==========================================
  Files              ?       43           
  Lines              ?     1108           
  Branches           ?        0           
==========================================
  Hits               ?      262           
  Misses             ?      846           
  Partials           ?        0           

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