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)
compiletest: Remove all uses of `~str` from `compiletest`
librustuv: Remove all uses of `~str` from `librustuv`
libfmt_macros: Remove all uses of `~str` from `libfmt_macros`
libserialize: Remove all uses of `~str` from `libserialize`.

Had to make `struct Tm` in `libtime` not serializable for now.
libgetopts: Remove all uses of `~str` from `libgetopts`
doc: Remove all uses of `~str` from the documentation.
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.
auto merge of #14135 : gereeter/rust/two-way-search, r=brson

This changes the previously naive string searching algorithm to a two-way search like glibc, which should be faster on average while still maintaining worst case linear time complexity. This fixes #14107. Note that I don't think this should be merged yet, as this is the only approach to speeding up search I've tried - it's worth considering options like Boyer-Moore or adding a bad character shift table to this. However, the benchmarks look quite good so far:

    test str::bench::bench_contains_bad_naive                   ... bench:       290 ns/iter (+/- 12)     from 1309 ns/iter (+/- 36)
    test str::bench::bench_contains_equal                       ... bench:       479 ns/iter (+/- 10)     from  137 ns/iter (+/- 2)
    test str::bench::bench_contains_short_long                  ... bench:      2844 ns/iter (+/- 105)    from 5473 ns/iter (+/- 14)
    test str::bench::bench_contains_short_short                 ... bench:        55 ns/iter (+/- 4)      from   57 ns/iter (+/- 6)

Except for the case specifically designed to be optimal for the naive case (`bench_contains_equal`), this gets as good or better performance as the previous code.
auto merge of #14216 : kballard/rust/macos_precise_time_ns, r=alexcrichton

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.
term: Don't run the code example, just compile it

This is blocking a snapshot because apparently the test fails on the bots.
auto merge of #14257 : alexcrichton/rust/fix-snap, r=huonw

This is blocking a snapshot because apparently the test fails on the bots.