debian changelog hack

put dummy UNRELEASED entry in changelog before build with dch -v
"version" "localbuild". This has the "papercut" of repeating the
"local build" bullet in the same entry each time the package is built.
!hurd-any for dependencies not available in debian hurd (libva,libv4l)
recommend libgl1-mesa-dri and suggest libaacs0
Better changelog hack in separate script called from ./update.

dpkg-buildpackage reads the changelog before ever calling
debian/rules, so its not a good idea to change it from there. Move
this to a separate script called from ./update which does not depend
on any debian-specific commands.
recommend video acceleration libraries
remove libwayland-dev build dependency
This is not enough to enable Wayland support on it's own.
You also need libxkbcommon-dev which is not universally available.
Add stuff to the README.Debian file describing differences
with the official Debian package. Also add instruction for
enabling Wayland support on Debian testing/unstable
(the only place it natively works).
Merge github.com:kevmitch/mpv-build
upstream merge