Revert "Remove incomprehensible Debian magic"

This reverts commit ba60c400ae5c69bd8b7f6c1368e6e8c6bfb42f24.
Bring back a waf-compatible deiban build system

For override_dh_auto_install, just tell waf to install the files under debian/mpv.

The main problem was that the script names clean,build,install in the
root directory collided with makefile targets in debian/rules which lead
make to do nothing since they appeared already up-to-date. .PHONY wasn't
enough since the targets are implicit via the % operator. I had to
explicitly declare the problematic targets AND list them as .PHONY
build more features in debian package including custom-built fribidi

* build fribidi for the debian package
* add dependencies to debian package taking cues from the official debian version
  enable everything except:
  + libsdl2 (not available in wheezy or precise)
  + libmpeg123 (build error on precise due to old version)
  + caca, radio interface, openal output, portaudio output,
    rsound/libroar/sndio input/output, sdl1, joystick, videoio.h/libpt
* additional ffmpeg features (and dependencies) are still to be handled
  manually by the builder using the ffmpeg_options file as described
  in README.rst
* adjust debian/changelog so building works on both debian and ubuntu
  (tested on saucy,precise,wheezy,sid amd64)
* tweak debian parts of README.rst
take fribidi build out of the debian pacakge and replace it with a
dependency on the debian pacakge libfribidi-dev
Merge remote-tracking branch 'origin/pr/17'