search: fix XSS vulnerability in search results

The search feature did not correctly escape all arguments when displaying
search matches and linking to the corresponding files.

An attacker that can control the contents of a repository could thus cause
a cross-site scripting (XSS) vulnerability.

Fix the problem by removing the overall h.literal call that is only needed
for the HTML entity » and splitting the link instead.

We take the opportunity to improving the destination of the part before
» which is the path to the repository. Instead of pointing to the
search result, point to the repository itself.
The part after » remains linked to the file containing the search
match.

Reported by Bob Hogg <wombat@rwhogg.site> (thanks!).