Add a custom Reline color scheme to the `Core::CLI::RubyShell`

[postmodern]

As of reline 0.4.0, reline now supports custom color schemes for the tab-completion menu. Ronin could customize the default cyan background + grey text + magenta highlighted text completion menu.

[AI-Mozi]

Something like that?

[postmodern]

@AI-Mozi nice! We should probably think about the color scheme.

[AI-Mozi]

Oh.. I thought you want a cyan background + grey text + magenta highlighted text 😅 I'll play with it a bit, but I think the black/white/gray/navy color pallet is associated with ronin.

[AI-Mozi]

@postmodern what do you think? I like that red background for highlighted option as it matches the irb(ronin-test)>

[postmodern]

@AI-Mozi I played around with some different color schemes. Here's white text on gray:

          Reline::Face.config(:completion_dialog) do |conf|
            conf.define :default, foreground: :white, background: :gray
            conf.define :enhanced, foreground: :black, background: :white
            conf.define :scrollbar, foreground: :white, background: :gray
          end

and here is white text on black:

          Reline::Face.config(:completion_dialog) do |conf|
            conf.define :default, foreground: :white, background: :black
            conf.define :enhanced, foreground: :black, background: :white
            conf.define :scrollbar, foreground: :white, background: :black
          end

Here's what white on gray with red highlighting looks like in my terminal:

Thoughts on which one is better?

[AI-Mozi]

white on gray with red highlighting does not look as good as in my terminal.. Maybe just white text on gray?

[postmodern]

@AI-Mozi yeah I'm liking both white text on gray and white text on black.

[AI-Mozi]

@postmodern I'll check which one looks better in my terminal, and I'll chose it

[postmodern]

Implemented by PR #57.