Cython runtime and compile target
I have been looking at Python runtime and examples for a while, and came to conclusion: probably best way to improve its performance by a significant factor is to cythonize it. 

Drawbacks: pypi manifest would need to include `cython` as dependency. This is a simple and quite reasonable tradeoff, little code added and much performance gained.

Construct is currently preparing to get into 2.9 version and cythonize itself. You might want to wait until then, to see benchmark comparisons and so I can learn/refresh how to code it. Then it will be easier for me to implement it in Kaitai as well. Kaitai benchmarks also need complete overhaul before this. 
