Compression context
When compressing many times,
it is recommended to allocate a context just once,
and re-use it for each successive compression operation.
This will make workload friendlier for system's memory.
Note : re-using context is just a speed / resource optimization.
It doesn't change the compression ratio, which remains identical.
Note 2 : In multi-threaded environments,
use one different context per thread for parallel execution.
