BigDFT Mac CI

This project uses github actions to verify we can compile and run BigDFT on Mac platforms.

It includes two rc files:

• mac_gcc.rc
• macc_clang.rc which choose between clang and gcc for the C/C++ compilers.

The install.sh script does the setup using homebrew, and then compiles. It takes one argument, either gcc or clang. Likewise, the test.sh script accepts either gcc or clang as an argument.

Anyone wishing to install it on their own computer might read the install.sh script and perform the same commands.