This is a copy of libtsm from the kmscon repository. It has no external
dependencies except glibc. libxkbcommon should be provided during
compile-time. If not, a fallback header is used.

The library interface is not stable, yet! There is still a lot to do
before we release libtsm-1.

Signed-off-by: David Herrmann <dh.herrmann@gmail.com>