(#7564) Finish templates

This is a rebase of the following commits:

• (#7563) Add a template for manpages

In order to generate manpages in a reasonably maintainable way, we need
to format text from the Faces help API for use with Ronn
(https://github.com/rtomayko/ronn/).

This commit adds a man template to the help templates folder; it has
been verified to generate Ronn-friendly input text. It isn't currently
called by any applications, but can be demonstrated by exchanging it for
face.erb.

• (#7634) Change ERB trim mode used in the Faces help API

<%= something -%> tags (note the minus) are unavoidably necessary at at
least one point in the Faces help templates. ERB objects instantiated
with the % trim mode will blow up horribly whenever one of these tags
appears.

This commit changes the trim mode to - and refactors all help
templates accordingly.

• (#7563) Refactor short help templates

This commit attempts to bring the short face and action help templates closer to the goals of fitting cleanly on one screen, fitting the prevailing *nix aesthetic, and being useful without overwhelming the user.