Add support for Part 15 to the JPEG 2000 (HT) decoder

This proposal aims to implement an ISO ITU-T Rec. T.814 compliant High Throughput jpeg2000 decoder for ffmpeg. The new jpeg2000 standard while being an improvement over the 1992 standard comes with a high computational complexity that makes it non-viable for current mainstream CPUs The main part being the context based binary adaptive arithmetic coder which manipulates bits(not bytes) hence has a high overhead. Part 15 of the spec seeks to replace that with a simpler and faster scheme for a high throughput decoder. This proposal seeks to implement a fully compliant ISO ITU-T Rec. T.814 for ffmpeg. Deliverables - A complete jpeg2000 decoder implementing the part 15 of the decoder for ffmpeg