Create a proper command-line interface

[mojavelinux]

Create a proper command-line interface to give the user greater control of the script.

Features should include:

• separate library from cli invoker
• usage text
• version text
• pass configuration options
• specify output file or directory

[mojavelinux]

Perhaps we can use a (simple) cli library like:

• https://github.com/leejarvis/slop
• http://trollop.rubyforge.org/
• https://github.com/mdub/clamp

[mojavelinux]

Once this is done, I think we can close https://github.com/asciidoctor/asciidoctor/issues/168.

[FranklinYu]

I would like to help this. Do you have any preference among the three options?

Some data for analysis can be found on Ruby Toolbox:

• slop is the most popular one. It looks similar to Ruby’s built-in optparse.
• trollop has been renamed to optimist.
• clamp is still maintained as well. This is more like a CLI framework, not only an argument-parsing library. Similar to Thor.
  • Homepage mentions clip (probably dead) and main (less popular).

By the way, the category Command Line Option Parsers and Scripting Frameworks may have some interesting choices.

[mojavelinux]

I don't like dependencies, so I prefer it be done with Ruby's stdlib. You can find an example to draw from in the kramdown-asciidoc project. See https://github.com/asciidoctor/kramdown-asciidoc/blob/main/lib/kramdown-asciidoc/cli.rb