A short summary of changes:
* Add some basic tests for UChild and the run methods.
* Try more often in a fixed interval to create the tempfile for CapturedOutput.
* Fix drop order of struct fields for better cleanup of temporary files/dirs.
* Mark UChild::wait_with_output and UChild::pipe_in_and_wait_with_output deprecated
* Make CapturedOutput private
* Panic in stdout_all, stdout_all_bytes etc. if output is not captured.
* Rename some methods, refactor, clean up, fix documentation, add try_... methods
This is part of fixing the tee tests. 'yes' is used by the GNU test
suite to identify what the SIGPIPE exit code is on the target
platform. By trapping SIGPIPE, it creates a requirement that other
utilities also trap SIGPIPE (and exit 0 after SIGPIPE). This is
sometimes at odds with their desired behaviour.
Report errors properly instead of panicking.
Replace zero_copy by a simpler specialized private module.
Do not assume splices move all data at once.
Use the modern uutils machinery.
Remove the "latency" feature. The time it takes to prepare the buffer
is drowned out by the startup time anyway.
yes: Add tests
yes: Fix long input test on Windows
