add usage + examples to help text

[lenscas]

Make it possible to show how to use a command as well as an example without manually putting it in the help text, so the help command can infer the rest. (Like how serenity does it)

lets take the prep_ban command for example. All I have to write is:

usage: {user},{amount_of_messages},
example @thanks_bot 10

and the output is:
Usage: prep_ban {user} {amount_of_messages}
Sample usage: prep_ban @thanks_bot 10

This will require changes in

• src/help.ts to display this new data
• src/command.ts to edit the command type to allow for this.
• every command to give this new information (Can become its own issue later.)