Also, error-out when no duration is available.

When analysing logs spanning over years, with monthly graph points.

They are more concise than hits per error code when details error is
requested.

Embed main.js. It's too small to justify doing a python module out of a
command-line executable.

Slowest page list is cluttered by temporary issues not representative of
service.

Because "hits" needs a "per $period" to be meaningful.

Add axis label (requires flot "axislabel" module).
Workaround default axis label color.
Save horizontal space between labels.
Provide minimal interval between ticks so label don't overflow on
each other.
Provide label width for Y axis so consecutive graphs are correctly
lined up.

Also, rename storage to be easier to understand in --help output.

So line count remains visible.

With (hopefully) appropriate settings.