Fix: [os.process] setting pipe mode on Unix.
Change: [os.process] minor change.
Fix: [os.process] makefile.
Change: [os.process] Process.kill() to Process.terminate() supporting SIGTERM on Unix.
Fix: [os.process] typo.
Change: [os.process] minor simplification.
Fix: [os.process] minor fix.
Change: [os.process] added os::Pipe type, moved I/O from os::Process to it;
Add: [os.process] support for manual redirection of process streams, blocking I/O mode.
Add: [os] os.ATOMIC_WRITE_CAP, max number of bytes which can be written to any device atomically.
Add: [os] os.ATOMIC_WRITE_CAP doc.
Add: [os.fs] fs.rm() to delete arbitrary file objects.