Trying as much as possible to consistently:
- use a present tense predicate followed by a direct object
- verb referring directly to the functionality provided
(ie. not "add command that does this" but simple "do that")
- keep simple and to the point, leaving details for the long help
(width is tight, possibly even more so for translations)
Thanks to timeless, Martin Geisler, Rafael Villar Burke, Dan Villiom
Podlaski Christiansen and others for the helpful suggestions.
For non-html mimetypes it doesn't make much sense. This also fixes the
issue that highlight unconditionally adds a <link/> tag for its CSS to
the template's header (which is pointless in text/plain output).
