Instant payment feature

Hi!

I tried to make it as general as possible, that is you can potentially re-use the "CAPTURE_DELAY_PARTIAL" as an additional option (integer parameter) that can be provided so that user could specify WHEN an authorisation should be captured (in hours, IIRC).

Technically "instant payment" is authorisation with an implicit capture (delay = 0), so I re-used almost everything you have there for the authorisation.

Please tell me what do you think about it - if there are any mistakes/errors/bugs or something that should be changed.

And, once again, thank you for this gem! :+1: