Draft: Add lab on new module system

[WeeknightMVP]

This lab describes Cryptol's new module system, which has not yet been merged. To test it requires a workspace in which one can build Cryptol from source and access different Git branches. With these prerequisites, assuming cryptol-course and cryptol-specs are cloned or downloaded to the same directory, the following should work:

$ cd ~/workspace  # or whatever
$ git clone https://github.com/GaloisInc/cryptol
$ git clone https://github.com/GaloisInc/cryptol-specs
$ git clone https://github.com/weaversa/cryptol-course
$ cd cryptol-course
$ git switch new-module-system
$ cd ../cryptol
$ git switch functors-merge
$ ./cry build
...
$ CRYPTOLPATH=../cryptol-course:../cryptol-specs ./cry run
Cryptol> :m labs::NewModuleSystem::NewModuleSystemAnswers
labs::NewModuleSystem::NewModuleSystemAnswers>

[WeeknightMVP]

We should turn off CI for this branch until functors-merge is merged.