Add Dropbox API documentation links #16
Description
Most of the specifics about how the Dropbox API works is spelled out in its own documentation. Adding links to it would be useful to reduce our documentation "burden", as well as help bug-hunters find unintentional discrepancies between dropbox-go, and the official API.
Despite the go API being somewhat based on the Ruby SDK, the links should probably be to the core HTTP API's documentation (ie: https://www.dropbox.com/developers/core/docs#delta NOT https://www.dropbox.com/static/developers/dropbox-ruby-sdk-1.6.2-docs/DropboxClient.html#method-i-delta).