API Documentation?

[bjadamson]

Hey, it would be great if there was documentation for the API, so it's easier to understand exactly what the API is.

The "data" proxy object is really neat, but it's API is really hidden. It's not obvious for example how to do various things in the library, such as iterating over all the entities. Trying to learn how to use this project so far has required me digging through the example (and following headers to learn what magical macros are doing for me)

Creating this issue to track the lack of documentation for the API. Even just pointers to the relative classes, indicating which are intended to be use as part of the public API would be massively helpful.