Documentation for Thenable

[paulyoung]

I think it would be useful to have a brief description of what each method does.

[cbchouinard]

Paul, I'm on it, should release some docs by the end of the day

[paulyoung]

Cool, thanks.

Doc blocks above the methods would be fine with me. In my experience those are more likely to stay up to date due to the close proximity to the code itself, and can always be made accessible via a link in the README.

[bergie]

https://github.com/the-grid/Flowerflip/blob/wip-docs/README.md