WIP: Add Unix manual pages

[jtbx]

This pull request adds Unix manual pages for each luarocks command.
A large amount of the content in these manuals are derived from the output of the luarocks help command.

I have a few questions:

• Temporarily, I have put the manual pages in /man. What directory should they be in?
• In the luarocks.1 manual page, I ordered the commands by how useful I think they are, and how much they will be used. Is this okay?

I used the OpenBSD mdoc format over groff, as it is easier to write for manuals and requires no preprocessing.

Closes #1483.

[codecov-commenter]

Codecov Report

Patch and project coverage have no change.

Comparison is base (fae768f) 79.06% compared to head (e018e95) 79.06%.

❗ Current head e018e95 differs from pull request most recent head 069860c. Consider uploading reports for the commit 069860c to get more accurate results

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Additional details and impacted files

@@           Coverage Diff           @@
##           master    #1484   +/-   ##
=======================================
  Coverage   79.06%   79.06%           
=======================================
  Files          89       89           
  Lines       11065    11065           
=======================================
  Hits         8748     8748           
  Misses       2317     2317           

Impacted Files	Coverage Δ
src/luarocks/upload/api.lua	63.84% <0.00%> (ø)

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[daurnimator]

A large amount of the content in these manuals are derived from the output of the luarocks help command.

luarocks --help is derived using argparse (https://github.com/luarocks/argparse).
Should that library perhaps gain some sort of manpage/groff output?

[alerque]

@daurnimator That would be nice 😁

[jtbx]

@daurnimator Never used that library before but sounds good.