[RFC] Cleanup user documentation build

This PR does some cleanup in the Makefile of the user documentation.
The first commit makes `make html` work.
Also some generated files got deleted and the `*.1` files are converted to UTF-8.
If we're going to move this in `/<locale>/` subdirectories, might as well remove the `-<locale>` suffix from the files. Personally, I prefer to keep hierarchies as flat as possible though, if there isn't a burdensome number of files.