build-sys: fix .h.in usage in libblkid and libmount

Signed-off-by: Karel Zak <kzak@redhat.com>
libblkid: remove private function from docs

Signed-off-by: Karel Zak <kzak@redhat.com>
libsmartcols: add debug and version functions

Signed-off-by: Karel Zak <kzak@redhat.com>
libsmartcols: improve docs

Signed-off-by: Karel Zak <kzak@redhat.com>