Serve gzip encoded resources

Generally you want two things to happen:

1. serve files using #sendfile
2. serve gzipped versions resources

Compressing resources in memory saves bandwidth but is suboptimal since the whole resource needs to be loaded into memory.

Jetty implements this like this:

• if the Accept-Encoding includes "gzip"
• and there is a ".gz" version of the file (eg. you request "style.css" and there is "style.css.gz")

then the ".gz" version is served.