Add man-style help page renderers for Kart

[amalthundiyil]

Description

Add man-style pagers instead of click's default help page when calling --help. Run the kart init --help or kart clone --help command to see man pages with additional docs sourced from docs/pages/commands. The paging methods used are:

• For Windows - click.echo_via_pager()
• For POSIX - man <path_to_page>

While experimenting with click-man, I also tried using sphinx-click for generating man pages but couldn't get much out of it (see stackoverflow question).

Design

Related links:

• #658

Checklist:

• [x] Have you reviewed your own change?
• [x] Have you included test(s)?
• [x] Have you updated the changelog?

[rcoup]

@amal-thundiyil can you sketch out (a drawing) of the process(es) happening here? ie: what formats are used, and the tools/conversions that happen (during builds, rendering, etc).

[craigds]

Thanks for your persistence! 🎉