build: fix linking with --enable-static-build
rpi: initial commit

Setup the audio decoder, video decoder and video output basic code.

Add README on external dependency on pkg-config files for the firmware.

Add --rpi feature to the build system.
rpi: add list of supported video decoder codecs
rpi: fix building
rpi: add some audio decoders
rpi: remove some leftovers from the README
rpi: add omx common helpers
rpi: add license headers