librand: Remove all uses of `~str` from `librand`
libsync: Remove all uses of `~str` from `libsync`
libtest: Remove all uses of `~str` from `libtest`.
libterm: Remove all uses of `~str` from `libterm`
liburl: Remove all uses of `~str` from `liburl`
libcollections: Remove most uses of `~str` from `libcollections`
libnum: Remove all uses of `~str` from `libnum`