Add a help command

[Wilfred]

trafficstars

Using ? for help is a magit convention. Offer basic information on keybindings by using Emacs' built-in help.

Fixes #59

[Wilfred]

Hmm, this doesn't show all bindings, such as :.

[Bounga]

@Wilfred That's because you ask to show keybindings for monky-status-mode there's no : binding in this mode. That's a monky-mode binding.

I think that in monky-status we want to see both monky-mode and monky-status-mode bindings. When viewing logs we want to see both monky-mode and monky-log-mode bindings and so on.

What do you think?