Added (empty) Python library for interacting with ROBUST

[ChrisTimperley]

Having a proper Python library for interacting with the ROBUST dataset makes it a lot easier to write good Jupyter notebooks (and to write useful scripts that rely on common functionality). This PR creates a robust package inside the lib directory and adds a reasonable tox linting setup into the CI (i.e., flake8 and mypy).

[wasowski]

This is a great initiative. I think we should merge ASAP (that is as soon as @gavanderhoorn approves :) )

[ChrisTimperley]

This was a hard but valuable lesson in rebasing vs. merging on feature branches. I managed to resolve the situation via the following:

$ git reset --hard 35ba39b
$ git rebase master

The first command rolls back the commit history to the point before the git merge master occurred. This is fine since there were no changes beyond that point anyway. The subsequent commit then performs the actual rebase.

@wasowski We should be good to merge?

[ChrisTimperley]

(Note that I'm still in favour of squashing and merging the PR before going into master. I can squash locally, but that would destroy the commit history on this PR, whereas using GitHub's "squash and merge" retains it.)

[wasowski]

squashed and merged!