Add HTML to modules folder and parse module html

This adds better docs to the static page builder and
therefore targets (#118).

It’s part of #123 (v2.0) though and closes #129 when
merged.
Automatically name page files by object key.

This removes the `dest` key in the pages.json
and retrieves the filename automatically.

Unfortunately this adds another dependency as
we need to deep-extend the object but I think
this is worth it.

This is part of #131 and targets #123.