This PR does a lot, but is it mostly just moving things around
* Adopt a src directory structure for the project
* Allow for packaging of the code as a library called 'deepmem'
- Add setup.py, setup.cfg, MANIFEST.in
* Add an Apache License
* Add build-system information to pyproject.toml to make compatible with PEP 660
- c.f. https://www.python.org/dev/peps/pep-0660/
* Use setup.cfg console_scripts to define maps between old main functions and command line scripts
- e.g. main.py behavior is now available after install through running the command 'deepmem'
* Update README to refer to 'deepmem' instead of 'main.py'
* Add setuptools_scm[toml] to build-system information to generate _version.py on install from version control
This PR does a lot, but is it mostly just moving things around