Lazy zopfli compression

[3rd-Eden]

Zopfli is a new compression algorithm written by fine folks over at Google. It's compatible with gzip/deflate but manages to squeeze the file contents more then gzip. This results in a 1% extra saving on average compared to a gzip -9.

But the downside is that takes 2 to 4 orders of a magnitude longer then regular gzip. In order to prevent blocking of the node process we could start this operation lazily after we have done a regular zlib operation which is much much faster. So there might a few users that receive a zlib version and the rest after it would receive a zopfli version.