Merge branch 'tests' into develop
Added test config files.
Make response plugins explicitly call dest.writeHead()

This also adds a 'head' event, containing statusCode and headers.
You must now wait on this event to access that information. After
the 'head' event, the normal Readable stream events occur ('data', 'end', etc).

Some other smaller fixups snuck in too.
Warn about requests that take a long time
Merge branch 'writehead' into develop
Add metrics for ingress/egress/cache byte transfer
Merge branch 'transfer-count' into develop
Rename constants.
Merge branch 'rename' into develop
Add support for XZ compression
Don't require an accept-encoding header for gzip, since SPDY does not require it

Also, gzip a few other mime types
Allow passing mocha args to 'npm test' via $MOCHA_ARGS environment variable
Merge branch 'lzma' into develop
Add debug metrics output in dev environment. gh-10
Add custom StatsD console backend.
Add user-provided metrics clients.
Update metrics production settings.
Cleaner metrics debug output.
Fix config.
Move StatsD backend out of repo.