Added a coro, `remove()` which takes in a sole parameter, `member`.
This new coro will remove the reaction by the provided member from the reactions message.
`message.remove_reaction(reaction, member)` was not removed as to not introduce breaking changes.
Added property `colour` and alias `color` which returns the Spotify
integration colour (#1db954).
Technically Discord uses both (#1cb050 and #1db954) but it appears the
former is an official Spotify colour.