search view: implement istartswith operation for build_apropos_filter

Closes #40

See merge request !36

Fixes #40
Fixes a52bd52b

Autofocus search input on the landing page

See merge request !35

Add `search_autofocus` to context, this is used to decide if the
`autofocus` attribute is added to the search input element.

postprocess: match references with the section number entirely inside the formatting tag

Closes #39

See merge request !34

fixes #39

Some small CSS improvements

See merge request !33

Even on large screens, words in tables can be broken in unnatural places,
depending on how the browser allocates table width. Disable breaking
anywhere, and instead break only on word boundaries. This matches how man
pages are displayed in a terminal.

When several options share the same description (such as short and long
options), the descriptions can become misasligned. Make dt elements have
100% width to prevent misalignment. This matches how this markup is
displayed by man viewers.

Resolve .so links with .gz suffix

See merge request !30

Fix links to man pages with sections specified by capital letters

Closes #35

See merge request !32

Make monospaced text the same size as the rest of the text

See merge request !31

"1.2em monospace" is slightly smaller than 1em of any other text.
Use "monospace, monospace" as the font to workaround the browser quirk instead of explicitly setting the font size.

Refactor the anchorencode function

Closes #31

See merge request !29

Fixes #31

Fixes #34

Add secure headers

Closes #28

See merge request !28

Only allow content from ourself and disable iframes, javascript and <base> elements.

Closes: #28

Add Referrer-Policy, X-Content-Type-Options and X-XSS-Protection.

By loading the XframeOptionsMiddleware django sets X-Frame-Options to
DENY preventing the website to be framed.

Updates for v1.1

Closes #25 and #24

See merge request !27

see #24

This redirects users directly to the man page if there is a match for
the query, otherwise it opens the search form as usual.

fixes #25

Deployment

See merge request !26