Add --meta-tags command line option.

Render meta-data section at the bottom of class documentation.

Treat @author and @docauthor as meta-tags.
For these tags strip e-mail addresses from content.
For now this ability is not supported for user-defined tags.
Probably some formatting will be useful for custom tags too - I'd
just like to gather some real-world usage info on this, so marking
this option currently as experimantal.