Add a copy-on-write container.
Added Freeze trait to CowArc
Allow SIMD types in generics. Closes #10604
Add `extra::getopts::short_usage`

This complements `usage` by auto-generating a short one-liner summary
of the options.
Move semver out of libextra.

Done as a part of #8784.

Signed-off-by: OGINO Masanori <masanori.ogino@gmail.com>
std: Remove io::io_error

* All I/O now returns IoResult<T> = Result<T, IoError>
* All formatting traits now return fmt::Result = IoResult<()>
* The if_ok!() macro was added to libstd
extra: Remove io_error usage
syntax: Remove io_error usage
rustc: Remove io_error usage
compiletest: Remove io_error usage
glob: Remove io_error usage
green: Remove io_error usage
native: Remove io_error usage
rustuv: Remove io_error usage
rustdoc: Remove io_error usage
rpass: Remove io_error usage
std: Fix tests with io_error usage
extra: Fix tests with io_error usage
native: Require all results are used and fix fallout
rustuv: Require all results are used and fix fallout