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
libextra: Introduce typed arenas.

A typed arena is a type of arena that can only allocate objects of one
type. It is 3x faster than the existing arena and 13x faster than malloc
on Mac.
doc: Syntax highlight the cheatsheet
doc: Fix table format in cheatsheet
doc: Title guides consistently
mk: Start testing the cheatsheet
doc: Highlight the testing guide correctly
mk: Fix the naming of the windows installer harder

CFG_VERSION includes a bunch of VCS info in it that is not a valid
filename. CFG_RELEASE is just the version number.
doc: Title reference manual consistently
doc: Fix URL of libextra docs
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`.
Inline reexports in rustdoc

If a reexport comes from a non-public module, then the documentation for the
reexport will be inlined into the module that exports it, but if the reexport is
targeted at a public type (like the prelude), then it is not inlined but rather
hyperlinked.
'borrowed pointer' -> 'reference'
doc: Add libgreen and libnative to the index
doc: Add rustc and syntax to the index