Rollback accidental documentation changes

These probably happened during the merge of the commit that made `Copy` opt-in.

Also, convert the last occurence of `/**` to `///` in `src/libstd/num/strconv.rs`
Add doctests for `iter_mut` and `into_iter` of BTreeMap.

Add spacing as dictated by standard rust code style.
Remove references to traits that no longer exist

This specifically means:
- `Deque`
- `Map`
- `Set`
Update sample code to use `getopts::usage` in `print_usage`
Implement insert for RingBuf
Add support for equality constraints on associated types
Mostly non-behaviour-changing changes (style, etc.)
Reviewer comments
Slimmify BTree by replacing its internal Node type, which previously…held three separately allocated `Vec`s, with a manually allocated buffer. Additionally, restructure the node and stack interfaces to be safer and require fewer bounds checks.

Before:
test btree::map::bench::find_rand_100                      ... bench:        35 ns/iter (+/- 2)
test btree::map::bench::find_rand_10_000                   ... bench:        88 ns/iter (+/- 3)
test btree::map::bench::find_seq_100                       ... bench:        36 ns/iter (+/- 1)
test btree::map::bench::find_seq_10_000                    ... bench:        62 ns/iter (+/- 0)
test btree::map::bench::insert_rand_100                    ... bench:       157 ns/iter (+/- 8)
test btree::map::bench::insert_rand_10_000                 ... bench:       413 ns/iter (+/- 8)
test btree::map::bench::insert_seq_100                     ... bench:       272 ns/iter (+/- 10)
test btree::map::bench::insert_seq_10_000                  ... bench:       369 ns/iter (+/- 19)
test btree::map::bench::iter_1000                          ... bench:     19049 ns/iter (+/- 740)
test btree::map::bench::iter_100000                        ... bench:   1916737 ns/iter (+/- 102250)
test btree::map::bench::iter_20                            ... bench:       424 ns/iter (+/- 40)

After:
test btree::map::bench::find_rand_100                      ... bench:         9 ns/iter (+/- 1)
test btree::map::bench::find_rand_10_000                   ... bench:         8 ns/iter (+/- 0)
test btree::map::bench::find_seq_100                       ... bench:         7 ns/iter (+/- 0)
test btree::map::bench::find_seq_10_000                    ... bench:         8 ns/iter (+/- 0)
test btree::map::bench::insert_rand_100                    ... bench:       136 ns/iter (+/- 5)
test btree::map::bench::insert_rand_10_000                 ... bench:       380 ns/iter (+/- 34)
test btree::map::bench::insert_seq_100                     ... bench:       255 ns/iter (+/- 8)
test btree::map::bench::insert_seq_10_000                  ... bench:       364 ns/iter (+/- 10)
test btree::map::bench::iter_1000                          ... bench:     19112 ns/iter (+/- 837)
test btree::map::bench::iter_100000                        ... bench:   1911961 ns/iter (+/- 33069)
test btree::map::bench::iter_20                            ... bench:       453 ns/iter (+/- 37)
auto merge of #18028 : gereeter/rust/slimmer-btree-node, r=Gankro

...ated buffer.

Before:

    test btree::map::bench::find_rand_100                      ... bench:        29 ns/iter (+/- 2)
    test btree::map::bench::find_rand_10_000                   ... bench:        83 ns/iter (+/- 6)
    test btree::map::bench::find_seq_100                       ... bench:        30 ns/iter (+/- 1)
    test btree::map::bench::find_seq_10_000                    ... bench:        50 ns/iter (+/- 3)
    test btree::map::bench::insert_rand_100                    ... bench:       186 ns/iter (+/- 30)
    test btree::map::bench::insert_rand_10_000                 ... bench:       377 ns/iter (+/- 8)
    test btree::map::bench::insert_seq_100                     ... bench:       299 ns/iter (+/- 10)
    test btree::map::bench::insert_seq_10_000                  ... bench:       368 ns/iter (+/- 12)
    test btree::map::bench::iter_1000                          ... bench:     20956 ns/iter (+/- 479)
    test btree::map::bench::iter_100000                        ... bench:   2060899 ns/iter (+/- 44325)
    test btree::map::bench::iter_20                            ... bench:       560 ns/iter (+/- 63)

After:

    test btree::map::bench::find_rand_100                      ... bench:        28 ns/iter (+/- 2)
    test btree::map::bench::find_rand_10_000                   ... bench:        74 ns/iter (+/- 3)
    test btree::map::bench::find_seq_100                       ... bench:        31 ns/iter (+/- 0)
    test btree::map::bench::find_seq_10_000                    ... bench:        46 ns/iter (+/- 0)
    test btree::map::bench::insert_rand_100                    ... bench:       141 ns/iter (+/- 1)
    test btree::map::bench::insert_rand_10_000                 ... bench:       273 ns/iter (+/- 12)
    test btree::map::bench::insert_seq_100                     ... bench:       255 ns/iter (+/- 17)
    test btree::map::bench::insert_seq_10_000                  ... bench:       340 ns/iter (+/- 3)
    test btree::map::bench::iter_1000                          ... bench:     21193 ns/iter (+/- 1958)
    test btree::map::bench::iter_100000                        ... bench:   2203599 ns/iter (+/- 100491)
    test btree::map::bench::iter_20                            ... bench:       614 ns/iter (+/- 110)

This code could probably be a fair bit cleaner, but it works.

Part of #18009.
auto merge of #19391 : nick29581/rust/assoc-eq, r=nikomatsakis

r? @nikomatsakis 

cc @aturon (I think you were interested in this for some library stuff)

closes #18432
auto merge of #19569 : murphm8/rust/ring_buf_insert, r=Gankro

This is a first pass at insert on RingBuf. I tried to keep it as simple as possible. I'm not sure of the performance implications of doing one copy vs. copying multiple times but moving a smaller amount of memory. I chose to stick with one copy, even if the amount of memory I have to move is larger.

I believe this is part of #18424 

@Gankro mentioned this was missing.
auto merge of #19664 : tbu-/rust/pr_oibit2_fix, r=Gankro

These probably happened during the merge of the commit that made `Copy` opt-in.

Also, convert the last occurence of `/**` to `///` in `src/libstd/num/strconv.rs`
Start restructuring to support generalized where clauses etc.
Thread a id to `Obligation`
Move the list of region obligations into the fulfillment context.
Introduce predicates but don't use them.
Write code for registering region obligations (but don't use it yet).
Switch to using predicates to drive checking. Correct various tests --
in most cases, just the error message changed, but in some cases we
are reporting new errors that OUGHT to have been reported before but
we're overlooked (mostly involving the `'static` bound on `Send`).
Remove diagnostic errors that were yielding warnings.