Switch to faster compression library

I've been working on a compression library [fflate](https://101arrowz.github.io/fflate) for the past few months. It performs quite a bit better than Pako in most circumstances for both compression and decompression of DEFLATE, implements GZIP and Zlib wrappers, and supports offloading processing to a separate Worker thread to avoid blocking. This should allow for much more similar functionality to the Node.js module.

Although the binary output for the compression methods is often vastly different from true Zlib with fflate, this shouldn't really matter, since the output is still valid and works fine. In some cases, the output is larger at the same level, but always by under 5%, and in exchange performance can increase by up to 50%. In addition, the API is completely different to that of Pako and Zlib, so this package may require a major rewrite.

Overall, `browserify-zlib` can weigh less, achieve higher performance, and, in some cases, act more similarly to true Node.js package (i.e. not blocking with the callback variant) using this implementation. If the maintainers are interested, I can submit a PR with the changes.

P.S. It may be of interest to update the package to use [Pako 2.0](https://github.com/nodeca/pako/releases) even if fflate won't work here.

/cc @browserify