Remove unnecessary trailing commas.
auto merge of #12013 : Hywan/rust/doc, r=sanxiyn
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
syntax: Remove usage of io_error in tests
std: Fixing all documentation

* Stop referencing io_error
* Start changing "Failure" sections to "Error" sections
* Update all doc examples to work.
Fixing remaining warnings and errors throughout