+ Added antialiasing support.
    + Dithering, antialiasing and background mode can now be selected at
      runtime.
  * src/caca.c src/caca.h:
    + Renamed caca_dithering into caca_feature and extended the type to
      express background colour and antialiasing mode.
  * examples/demo.c:
    + Fixed a bug that disabled the sprite demo.
    + Draw solid flares.
  * examples/view.c:
    + Select antialiasing and background mode at runtime.