Auto merge of #43 - Ogeon:docs, r=Ogeon
Auto merge of #43 - Ogeon:docs, r=Ogeon

Write more documentation for Context and friends

 * Add some more info and examples to body parsing extension traits.
 * Give examples for how to access parts of the `Context`.

resolves #41
resolves #42

evnix/Rframe,evnix/Rframe