Refactor "Help" Command

[mathsman5133]

Discord.py redesigned and created how help commands work - some helpful links:

• https://gist.github.com/Rapptz/288294ca99fa1f042f0e39a92ddd88eb#news-post
• https://discordpy.readthedocs.io/en/latest/migrating.html#helpformatter-and-help-command-changes
• https://discordpy.readthedocs.io/en/latest/ext/commands/api.html#help-commands

This was way back before rewrite was released. Since then there has been at least 1 (ctx.send_help) helper added that works with an updated implementation of help, but not with ours.

A refactor to subclass the HelpCommand class and friends shouldn't have any outward-facing changes, but it will clean-up and update the code to be compatible with any future helpers or releases, as well as ctx.send_help and any others I've forgotten

I'd like to work on this if it's approved.

[MarkKoz]

This sounds good. You can work on it. I think @scragly may have had some ideas for how to improve it too.