Wider field for benchmark names

I hit the 30 character limit a few times already, bumping it to 100.
New admin action for Reports: recalculate

After doing a bulk upload of benchmarks, possibly not in chronological
order, the reports might show changes wrt. to the wrong previous commit.
Then, triggering this action for all reports helps.
Aggregate report per unit_title, not per unit

If we have several very different things (Buildtime vs. Runtime) with
the same unit (seconds), we want to keep them separate.
Bugfix: Changes view for old revisions

This fixes #168.
Also include values "0" in the reports

If no value is reported, then there wouldn't be a Result object, so a
value of 0 is valid.
Merge pull request #169 from nomeata/submit

My upstreamable changes so far
Closes #168
Support for +∞ and -100% in change columns

This fixes #170.
Fix 0/0=0 in change column
Implement “latest significant results” table and feed

This fixes #171
Refactor feed generation a bit
Fill the RSS feeds with a bit more content

Especially the summary is useful
Include the full changes table in the feed

(by putting it into a template of its own)
New color "light green" for positive trends

to distinguish them from non-trend improvements.
Simplify classification logic for the summaries

(changes results before trends, averages before individual results)
Integrate code review
Merge pull request #172 from nomeata/submit

Two more changes