Write user manual

In fithesis3, I have written a user manual, which complemented the technical documentation. Between the release of fithesis3 and fithesis4, I received multiple requests for an HTML version of the user manual, which were difficult to realize due to the low-level typographic programming involved.

In fithesis4, @xvrabcov and I removed the manual, which was getting out-of-sync with the code base, on the basis that all relevant information for the user should be present directly in the example document for fithesis. However, since the release of fithesis4, I have had numerous requests for a manual from students.

If we were to create a new user manual, here are some considerations:

1. The manual should be easy to convert to both HTML and PDF. Markdown seems like a good choice.
2. The text of the manual should be part of fithesis.dtx and the other *.dtx files, so that it is easily kept in-sync with the current state of the code base.

Other ideas are welcome.