Indicate unsupported versions in RSS feed
Use a proper database field for beta releases

This replaces the previous ugly hack where beta versions had a negative number
as latestminor, giving a much cleaner model.

Requires SQL:
ALTER TABLE core_version ADD COLUMN beta boolean NOT NULL DEFAULT 'f';
ALTER TABLE core_version ALTER COLUMN beta DROP DEFAULT;

(Yes, we really need to move to something that can do automatic migrations)
Explicitly list beta and development versions in docs as "devel"

Previously we listed both those as unsupported, which confused some users
particularly with new beta releases. While they are technically not supported
yet, it gave off the image that specific features would not be in newer
versions anymore, since they got listed as unsupported.

In passing, fix the style of the links in case they only exist in old
versions, which would put an extra | character in the version list.
Indicate survey posting date on survey result page

Fixes #207
Include development and beta versions in search indexes

This includes both the sitemap used by google and friends and our own
site index, which uses the sitemap to decide which URLs to crawl.

Fixes #171
Closes #172
Don't generate broken links to /docs/0.0/ in the sitemap

Generate proper /devel/ URLs, and then exclude them again in robots.txt
so we don't include them in google results, but we do include them in
our own.
Make an actual foreign key between docs versions and core versions

This was originally not done because we had a lot of old legacy data
that didn't have entries in both tables. This is no longer the case,
and the docloads script already enforced that it couldn't happen again.

Requires SQL:
ALTER TABLE core_version ADD CONSTRAINT version_unique_tree UNIQUE(tree);
ALTER TABLE docs ADD CONSTRAINT docs_version_fkey FOREIGN KEY (version) REFERENCES core_version(tree);
Get the list of documentation versions out of the database

Instead of having to update this list manually in multiple places when
releasing new versions, just take the information out of the database
where it has to be anyway.

Fixes #90
Closes #93

Also make the code automatically pick up wich PDF files exist in the
static checkout, and auto-detect their size, both A4 and US sizes. This
removes yet one more manual step, yay!

Fixes #163
Move docs templates into the docs/ app, now that they are not plain pages
Use same header in manual list and manual archive
Expire list of docs and manuals when versions are updated
Oops, we're not supposed to include supported versions in the archive
Fix links to frontpage of documentation for old versions

I forgot that old versions have strange names for their homepage, and
we only switched to index.html in 7.2.
Fix strange float casting problems in python