Add TOC, typo fixes

Table of Contents generated with DocToc, http://doctoc.herokuapp.com/. I've removed level-3 headings, which were generated for most methods because their description starts with '###'. Might be worth considering making those plain text.
Trim TOC
Inlined state diagrams for canceled and paused

Didn't inline the complete state diagram after the very first one because the user is warned that it might look "crazy", so leaving it as a linked image seemed more fitting.
Merge pull request #6 from dandv/patch-1

Add TOC, typo fixes