"zlibd" module for zlib decompression, based on miniz implementation

This is initial rough implementation based on #741 proposal. Unfortunately, tinfl implementation of miniz isn't as minimal as it seemed - while it was advertized as not requiring any additional buffers besides target buffer, actually it needs decompresson context object, and that's whole 11K.

So, this will need further elaboration, but let's have at least something now. The main question for this review is how to handle 3rd-party source code drops. In this case, it's just single file, but for example for #13 there might be bunch of small files. Do we want to use subdirs under extmod/ to organize them?