Documentation title customization

[johnfairh]

Continuing #1065.

This adds the module version number to the docs title if one is configured, and also adds a --title flag to let users completely customise the docs title.

In the various themes:

Specs changes to show results of various options.

[captainbarbosa]

Whoa, was literally looking for this a few hours ago. Thanks!

[friedbunny]

Yay! Happy to see #411 being addressed — thanks @mbalex99 and @johnfairh. 🙇

[SzymonMatysik]

What if i'd like to change those in red rectangles? They're still identical like module name, when i'd like to customize it.

[johnfairh]

In the jazzy themes, that breadcrumbs line refers to Swift object names -- the thing outlined in red above is the Swift module name (ie. for import). You'd need to post-process the html or create a new theme by copying the one you want and using --theme.