Restructure and add packaging metadata

[adigitoleo]

closes #5

TODO:

• Add version ranges in install_requires (setup.cfg)
• Specify parallelism framework dependency
• Check that shell scripts are found by console_scripts (setup.cfg)
  Using scripts = specifier instead
• Use setuptools_scm to source package version from git tags

[adigitoleo]

Eventually the README can be updated with new installation instructions:

1. Bare minimum, using multiprocessing from stdlib: pip install pydrex
2. With a third party multiprocessing library, e.g. pip install pydrex[ray]
3. With ray, matplotlib and SVML support: pip install pydrex[ray,plot,svml]

For now, it's not on PyPI so the installation should work like this:

1. Clone/download source files
2. Navigate to source root (where the setup.cfg is)
3. Run pip install .[ray,plot,svml] (i.e. replace pydrex with . in the above)

That should get the dependencies and set up an importable python package called pydrex.

[adigitoleo]

Not quite ready, pip is yelling at me about a few things...

[adigitoleo]

OK should be good to go now

[adigitoleo]

Closing until the Next Big Rewrite (TM), there's a lot more to do before packaging.