mk: Fix formatting of docs.mk
doc: Update style of index, organization and trim out some excess.
Add Pointer tutorial, rename borrowed pointer tutorial.
doc: Fix tests in pointer guide
auto merge of #11364 : brson/rust/docs, r=alexcrichton

This reorganizes the documentation index to be more focused on the in-tree docs, and to clean up the style, and it also adds @steveklabnik's pointer guide.
Renamed Option::map_default and mutate_default to map_or and mutate_or_set
auto merge of #10854 : Kimundi/rust/result_compose_map_mutate_or, r=alexcrichton

This implements parts of the changes to `Option` I proposed and discussed in this thread: https://mail.mozilla.org/pipermail/rust-dev/2013-November/006254.html, and on IRC.

In short, the string "default" should not be used in any context that has nothing to do with the `std::default::Default` trait.

This PR consists of this change:
- Renamed `map_default -> map_or` and `mutate_default -> mutate_or_set`.
Fix leaking trait imports across modules

Turns out the pass in resolve was a little too eager to travel back up the
hierarchy chain when looking for trait candidates.

Closes #10465
rustc: De-indent portions of middle::resolve

It's a little prettier to look at now
std: Fill in all missing imports

Fallout from the previous commits
Fix remaining cases of leaking imports
stdtest: Fix all leaked trait imports
extratest: Fix all leaked trait imports
Fixup the rest of the tests in the compiler