ALS encoder

For the last several months, Thilo and I have been working on an ALS encoder. I'm quite happy with the results so far. It is nearly finished, minus a few optional features. It is generally much faster than the ISO reference encoder (twice as fast in default mode) and usually gets slightly better compression. Once we get the encoder to the point where we have all of the features implemented that we want and as many bugs worked out as we can, we will do massive amounts of benchmarking. I'll try to post any interesting results here.