Convert the English documentation to ReStructuredText.

The image resources for the html files have been moved to not
be on a higher tree level where images for all subdirs of the
English docs are stored. Now the ones for a particular subdir
reside in the pictures/ directory inside of that subdir.

The page generated from faq.htm is now 'faq_historical.rst'

faq_historical.rst has not been proofchecked and probably never
will be. Reason being, it appears that most of the faq_ pages and
possibly a couple other pages in maindir/ were the result of
faq.htm being broken apart into separate pieces, because there's
a ton of duplicate content in faq.htm.

I'm not really enthused to do all that work all over again, when
the information is mostly contained in other files. So it'll be
left as-is, waiting to be deleted upstream at a later time. If
there's something to salvage from it, then that can be decided
at that point.