Optimize inflate() function.

[mbebenita]

A hand tuned version of inflate (https://gist.github.com/mbebenita/be701a32a07afad4ff93) yields nearly a 2X perf improvement, from 1.2s to 0.6s when decompressing all classes in a large jar file. Zlib via emscripten is about 1.4s.

The referenced gist is a very hacky / quick dirty experiment to find out if there is room for improvement, and it looks like there is.