Fixed README issues.

[Quahu]

Hopefully that's everything (and not too much)!

Here's what I've done:

• updated the table of contents to refer to headers instead of the dummy <a> elements
• fixed all typos I could find, both outside and inside code blocks
• wrapped all type names in inline code, e.g. SomeClass
• reworded some sentences that were incorrect or confusing
• fixed code that wouldn't compile
• redone the non thread-safe operation list (this one) by essentially grouping the actions in a way which I think is slightly easier to digest

[Doraku]

My god am I this bad at English or just documentation :D thanks a lot for this!