Feature: add in style parameter

[TRex22]

What does this PR do?

• Implements the ability to modify the console styles of the progress bar
• List the available styles
• Specs
• Readme

Available Styles

[paul]

This change I'm less excited about. It seems like a fairly complicated feature and I'd much prefer keep this gem as light as possible. I might be open to having a separate "theme" accessor, that's either a hash or a ProgressBar::Theme struct, which contains colors and delimiters (from your previous PR).

It might work something like this:

MY_BAR_THEME = {
  foreground: :green # or 32
  background: :black # or a number
  bar_character: "#",
  delimiter: "[]"
}

bar = ProgressBar.new(100, theme: MY_BAR_THEME)

big_list.each do |item|
  do_stuff
rescue 
  bar.theme[:foreground] = :red
  # or bar.theme = MY_ERROR_THEME
ensure
  bar.increment!
end

Alternatively, instead of ProgressBar having to know anything about color, there could just be :prefix and :suffix attributes on the theme, and you could set them to \e[32m or whatever other terminal colors you want. The same could be done with the delimiters, like delimiters: ["\e[36m[\e[38;5;240m", "\e36m]\e0m"], which would give even more control over how to make the bar look.

WDYT?

[TRex22]

I initially didnt like the second idea but its growing on me. It would allow anyone using this gem to decide and use their own modifiers. It would also mean a hardcoded set of styles based on the limited default console set wouldnt be needed.

I wouldnt go for the first idea because I feel its even more restrictive than the first. I would rather leave style decisions to whomever is using the library.

I will update this to use the prefix suffix idea but have a bit more of an extensive readme section to help anyone get started. Such as including the screenshot above.

[TRex22]

Im going to close this PR and re-do it using the prefix and suffix ideas