Update manual

Because I'm still :mask: :mask: :mask: , I figured some mindless tasks would be better than trying to finish the ownership guide. 

The manual has long been waiting for some :heart: :heart: :heart: , and so I gave it a quick once-over. I made small commits in case any of the changes are a bit weird, I mostly did a few things:

1. changed 'manual' to 'reference.' I feel like this name is better. If it's not, It's not a huge deal. it shouldn't be `rust.md` though.
2. word wrapped everything appropriately. Changes 1&2 are in the first commit, so that its' easier to see the changes in the later ones.
3. fixed other small style issues
4. removed references to things that are in the standard library, and not the language itself

There's still lots of gross in here, but I didn't want to pile on too too many changes.

/cc @brson @nikomatsakis