Change to qpl job queue

[gbtucker]

Should be better than using set number of single-use jobs for a number of reasons.

• Better compression ratio for large files.
• Generally better compression ratio: better balance of huffcode header size overhead (blocks too small) to following dynamic statistics in large files.
• Can hide much of memcpy overhead on compression by copying as blocks finish instead of waiting until end.
• Doesn't rely on metadata kept outside of binary protocol.