Vendor fprettify autoformater and add to CI

[danielhollas]

Unfortunately, fprettify autoformatter is not maintained much, and we need some fixes for it to work for ABIN. So we simply copy the source code with the fixes in the repo to make our lives simpler. The code can now be autoformatted simply by running

./autoformat.py

(assuming the configargparse Python module is installed.)

The formatter source code is vendored in fprettify/ (no need to review those files).

We now check the formatting in Github Actions, I've modified CONTRIBUTING.md accordingly.

[codecov]

Codecov Report

Merging #167 (f9f0615) into master (542b515) will not change coverage.
The diff coverage is 62.79%.

@@           Coverage Diff           @@
##           master     #167   +/-   ##
=======================================
  Coverage   92.37%   92.37%           
=======================================
  Files          43       43           
  Lines        6084     6084           
  Branches      741      741           
=======================================
  Hits         5620     5620           
  Misses        452      452           
  Partials       12       12           

Flag	Coverage Δ
unittests	24.67% <0.00%> (ø)

Flags with carried forward coverage won't be shown. Click here to find out more.

Files	Coverage Δ
src/abin.F90	93.12% <100.00%> (ø)
src/cmdline.F90	100.00% <ø> (ø)
src/force_terash.F90	97.02% <100.00%> (ø)
src/surfacehop.F90	95.60% <100.00%> (ø)
src/tera_mpi_api.F90	97.00% <100.00%> (ø)
src/utils.F90	98.18% <100.00%> (ø)
src/landau_zener.F90	90.03% <95.45%> (ø)
src/force_tcpb.F90	29.72% <6.25%> (ø)

[JanosJiri]

Seems to do nice formatting of the code.