clean up src/FCF/Broken and extract useful theory

[andres-erbsen]

`I would prefer to keep the non-building files in the repo for the following reasons:

They still can be useful illustrations (especially the examples).
There may be some argument in there that is needed in the future, and it would be easier to fix the file than to develop it from scratch. A person probably wouldn't think to look in the history for "almost working" theory.
That being said, some of the non-building files are definitely old junk that needs to be removed. So I suggest:

Leave these files in and exclude them from the build. If you like, you can move the non-building files to a separate directory to simplify the build.
Create a ticket (assigned to me) reminding me to go through and clean up these broken files. Useless ones should be removed, valuable ones should be fixed.` @adampetcher

The files are now under src/FCF/Broken, with non-building bits commented out.