Port chunk mode to new codebase

[chocolate42]

It's the last mode to port and would allow for a lot of old code to be removed. As the first mode to be implemented it's particularly clunky.

• Output thread is deprecated as the output queue can handle it
• MD5 thread is deprecated as hashing should be done whenever the largest blocksize of a chunk is analysed
• Currently parallelism is done via multiple chunks simultaneously, rework it to parallelise within a chunk and only process one chunk at a time. This will remove a lot of complexity
• Use of simple_enc will remove more complexity

Once ported tweak will be better, merge will exist, multithreading output encoding will exist. Chunk might still be viable.