This fixes#1247. It also regenerates the usage documentation, so that
styling fixex in that section (as well as other existing changes) make
it into the files in docs/.
the generation of those files was causing us way too much pain to
justify automatically generating them all the time.
those will have to be re-generated with `build_api` or `build_usage`
as appropriate, for example when function signatures or commandline
flags change.
see #384