Added substring searching benchmarks.

test str::bench::bench_contains_bad_naive                   ... bench:      1309 ns/iter (+/- 36)
test str::bench::bench_contains_equal                       ... bench:       137 ns/iter (+/- 2)
test str::bench::bench_contains_short_long                  ... bench:      5473 ns/iter (+/- 14)
test str::bench::bench_contains_short_short                 ... bench:        57 ns/iter (+/- 6)
Switched to the two-way algorithm for string searching

test str::bench::bench_contains_bad_naive                   ... bench:       300 ns/iter (+/- 12)     from 1309 ns/iter (+/- 36)
test str::bench::bench_contains_equal                       ... bench:       154 ns/iter (+/- 7)      from  137 ns/iter (+/- 2)
test str::bench::bench_contains_short_long                  ... bench:      2998 ns/iter (+/- 74)     from 5473 ns/iter (+/- 14)
test str::bench::bench_contains_short_short                 ... bench:        65 ns/iter (+/- 2)      from   57 ns/iter (+/- 6)
flate: add documentation
arena: add docs for Arena
num: expand crate documentation + add example
term: add docs and windows support

Closes #2807
syntax: update for libterm fallout
time: crate description
workcache: add crate doc block
test: update for term fallout
Add WinConsole docs
Update for master
Update for Box
Add a bang
Flush before applying console attributes
Fix example
Some fixes
auto merge of #13401 : cmr/rust/docs, r=brson

Adds docs where previously there were no docs. Also adds windows support to libterm.
auto merge of #14233 : pcwalton/rust/detildestr-morelibs, r=alexcrichton

r? @alexcrichton
Optimize and fix time::precise_time_ns() on macos

Use sync::one::Once to fetch the mach_timebase_info only once when
running precise_time_ns(). This helps because mach_timebase_info() is
surprisingly inefficient. Also fix the order of operations when applying
the timebase to the mach absolute time value.

This improves the time on my machine from

```
test tests::bench_precise_time_ns ... bench:       157 ns/iter (+/- 4)
```

to

```
test tests::bench_precise_time_ns ... bench:        38 ns/iter (+/- 3)
```

and it will get even faster once #14174 lands.