Allow conditional dependencies between rects when decoding
Some encodings only cause dependencies between rects some of the
time. Make sure we can allow parallel decoding of those rect that
aren't dependent on each other.
This implements the basic infrastructure for multi-threaded
decoding of rects. However there is just one thread reading data
and one thread decoding it. More logic is needed to safely decode
multiple rects at the same time.
We need to split these steps up in preparation for multi-core
support. Reading needs to be done in a serial manner, whilst
decoding can be done in parallel.
This also involved a rather large cleanup of the Tight decoder.
Delegate decoder object management to a separate class
Done in preparation for multi-core decoding. Keeps the complexity
out of the other classes. This also moves ownership of the
framebuffer in to CConnection. It's the CConnection object that is
aware of the threads and how to synchronise with them. Therefore
the ownership of the framebuffer must also be there to make sure
it isn't deleted whilst threads are working.