Structure save and load

See last commit for details.

Want to add

• [nice to have] The checkpoint / model save path could be exposed over argparse to a command line option, which makes training/loading a variety of models much easier

in next issue (backlog).

The checkpoints:

• Review the first draft of the README.md
• Add missing and edit already existing sections

in different issue to keep it clean :)

Closes #44 (closed)