The API documentation you linked is for 1.8 and 1.8 does support everything, regarding media - the media upload (library/add) and assign (playlist/library/assign) are the ones you’re looking for - which is described step by step in my guide linked by Dan.
Now, 1.8 does support adding/editing of all modules (not only media based), but it’s not documented yet - we’re in the process of doing that along with the tests for them.
Regarding 1.7 API, you can have a look here - http://xibo.org.uk/2014/02/19/scripting-xibo-content-management-a-brief-tour-of-the-api/ or http://xibo.org.uk/manual/en/api_library.html
You will find that, being a BETA, the 1.7 api is not as full featured as 1.8 and lacks documentation. For API use we’d recommend to either use 1.8.0-rc2 currently available or wait for full release.