[DOC] Add API.md listing all routes.
[DOC] Add subheaders for each api call.
[DOC] Began adding subheaders for api calls.
[DOC] Finish adding method, url as subheaders.
Merge branch 'develop' into api-doc
[DOC] Add first few json request, responses.
[DOC] Format API doc.
[FIX] retry failed payment.