* ./include/configuration.h: renamed MODULE_CONFIG_* macros into

* ./include/configuration.h: renamed MODULE_CONFIG_* macros into
CONFIG_*.
* ./include/configuration.h, ./plugins/gtk/gtk_preferences.c,
./plugins/filter/transform.c, ./plugins/filter/distort.c,
./plugins/filter/deinterlace.c: added an ADD_STRING_FROM_LIST()
configuration macro.
* ./include/modules.h, ./include/video_output.h,
./src/video_output/video_output.c, ./plugins/filters/*: added a
VOUT_FILTER capability. Having a clear distinction between VOUTs and
VOUT_FILTERs allows us to get rid of ugly hacks. The filters are also
stackable now (use --filter=foo:bar:foo etc..).
* ./include/configuration.h, ./src/libvlc.h, ./src/libvlc.c: clean-up +
added an ADD_USAGE_HINT() configuration macro.