shuffled files around so it can be built as a pip package

[emil-perhinschi]

• moved sources under src/
• created pyproject.toml, did not add "authors" or "maintainers" though
• changed setup.py to have the project name as tapsimple instead of pyTAP because the pyTAP name is already taken on pypi https://pypi.org/project/PyTap/
• changed .gitignore to

Did not upload anything to pypi.