The custom initrd format was originally useful when it was mounted,
however it has been extracted into the ramfs for a very long time and
has no advantages over the standard tar format which can be readily
created and modified using standard tools. The kernel initrd(7) support
already supports tar, so this change simply switches the format.
roff(7) dictates that "Each sentence should terminate at the end of an
input line." Instead of doing this, Sortix manpages (incorrectly) used
double-spaces to separate sentences.
Additionally, fix a few small typos.
