Core Gemini docs converted to text/gemini

[solderpunk]

Ahoy Geminauts!

Yesterday I converted the core Gemini documents, i.e. the protocol
specification, FAQ and best pratices documents, into the text/gemini
format, as only seems appropriate!  The Gopher version of the official
site now serves text/plain versions derived from the new text/gemini
originals using `fmt -s` to wrap lines.  The HTTPS version similarly
serves text/html versions derived from the text/gemini originals using a
Markdown converter and a little bit of sed.  The CSS styling of the
website has also been changed to make reading these long docs a little
more comfortable.

As part of this change, some URLs have changed.  Rather than the URLs
ending in .txt for all three protocols, they now end in .gmi, .txt or
.html as appropriate.  Also, the specification now lives at
specification.*** rather than spec-spec.***.  Redirects and symlinks
should avoid the breakage of any existings links or bookmarks, but if
you notice anything broken, please let me know!

Some changes to the actual content of the FAQ have also been made.

I will make some spec changes later today - nothing which has not
already been discussed here on the list.

Cheers,
Solderpunk