Convert file format descriptions to rst

Convert file format descriptions to rst

Convert the old HTML files about file formats to reStructuredText, and
merge them on a single page.  This is more or less a blind conversion.
No attempt is made to make them appear particularly nice, or to fix
outdated information.  But this works towards the goal of reducing the
number of distinct document generation mechanisms, and should make it
easier to restore functionality of linking to file formats from
generated pages for programs.

Now the only thing that remains in the old-html directory is the
flowchart.

Change-Id: I88bfbdf48f3ba870c9501ef933c03a947ea43635