Add to documentation

[qwergle]

I've added to the documentation. Still, there's quite a while to go. So far, I've added descriptions for the higher-level functions, a description for the Unicorn object, and descriptions for some of its methods. Still, the Constants section needs to be filled out (that will not be easy for whoever takes on that challenge), many Unicorn methods need descriptions, and a few need their descriptions to be more polished.

[AlexAltea]

Looks good, thank you!

Please remove the section on helpers (anything prefixed with __) as that's not meant to be consumed externally. I'll merge immediately afterwards.

[AlexAltea]

Actually, I was able to do so directly from GitHub, that's pretty cool. 😄

Merging now; thanks again!