Make compressible mime types configurable.

The compressor middleware now accepts a list of compressible mime types, defaulting to compressing any type. Wildcards are supported.
Minor improvements

--HG--
extra : amend_source : 1f16ab8ce27a85531b3a2793c3fc8212c77d5b3a
Add utility code for computing hex representation of byte stream
Add a middleware to set ETag header on responses
Remove annoying warnings when compiling with JDK 8