Zippy: a dependency-free Nim implementation of deflate, gzip, zlib, zip

[b3liever]

Great effort, much appreciated! Btw I noticed throughout the code:
    
    
    when defined(release):
      {.push checks: off.}
    
    Run

It's a bit cheeky :) Wouldn't it be better if we follow default conversions in 
nim code?