Don't Include Proof General in this Repo

[bkc39]

It is ridiculous to have the entirety of Proof General in courseware/.emacs.d. What we should do is either:

• Add a setup script to download an configure it on VM startup.
• Update pkg.el to download the package to the relevant directory and add the load to the config.

Unfortunately Proof General isn't on MELPA so we have to do one of these things. But this will drastically reduce the size of this repo. More importantly it reduces it to code we actually wrote =)

[bkc39]

If you approve of #11 we can consider this closed.

[bennn]

al-right