chore: add ci.yml

[vil02]

Fixes #13.

It works on my end, cf. vil02#1, vil02#2 (please have a look to the action runs).

The CMakeLists.txt is not perfect, but I think it is good enough for now:

• scans the modules, tests and example directories for *.f90 files,
• all of the tests and examples are linked with all of the modules,
• the tests and the examples, have pretty unique name: even if there would be two files with the same name in tests/sorts and tests/some_other_algorithms this would not cause any problem.

When this will be merged, there are few things on the to do list:

• make of all of the files in the other directory proper modules and add tests for them,
• fix the warnings (currently there are few unused variables),
• add the -Werror flag,
• generate coverage reports.

[SatinWukerORIG]

Hello @vil02
Great work! However there is a conflict in the modules.