Add PWmat module (io, calculator)

Here: Add IO and calculator modules to PWmat which is a DFT software.

PWmat is a DFT software that runs on GPU/CPU, developed under the leadership of processfor Lin-wang Wang. I have been using PWmat for high-throughput computing and I hope to contribute my code to help more people conveniently use PWmat.

This submission includes some basic features:

1. Reading and writting structural files, which named 'atom.config'/'final.config'.
2. Reading the output file which is named REPORT.
3. PWmat calculator (its function is not yet perfect compared to VASP calculator).

I am working hard to familiarize myself with the ase code, and I will continue to improve these modules in the future.

Checklist

• I am familiar with ASE's contribution guidelines.
• Doc strings in code changed in this MR are up to date.
• Unit tests have been added for new or changed code.
• Issue is resolved via "closes #XXXX" if applicable.