Package code and make pip installable

[cthoyt]

Would you be interested in a PR that reorganizes the structure of the code to follow python community standards such that it can be installed with pip install chempiler? This would reduce a lot of the need for appending to the sys.path and using frame inspections, while making the code much cleaner and easier to navigate.

I could also show how the client could be automatically installed with a vanity command using Python's entrypoints so you could run chempiler directly from the bash