Handle OAuth errors more nicely
Change all tokens to use options

Transients are unreliable, and I'm an idiot. :)
Move the template to oauth/authorize

This breaks existing stuff. Deal with it, please.
Move nonces to an option

Props @maxrice for this, stolen from the WooCommerce API
Parse form parameters to the authorization handler
Add flowchart on how authorization should work
Remove plugins_loaded hook

This is temporary, but it breaks /oauth/access_token at the moment.