[trunk] fixes issue #357. MCT is automatically disabled when
subsamppling is detected.
memory cleanup
allocate code block memory in one go, for each tile
added timing code to compress
document
for t1 encoder, use tile data rather than creating a new buffer for each code block and copying into

that buffer
do dc shift in mct for standard lossy and lossless transform
moved max calculation to avoid re-iterating through data
t1 cleanup