Handler that serves as the basis for content encoding implementations.
Encoding handlers are added as delegates to this handler, with a specified server side priority.
If a request comes in with no q value then then server will pick the handler with the highest priority as the encoding to use, otherwise the q value will be used to determine the correct handler.
If no handler matches then the identity encoding is assumed. If the identity encoding has been specifically disallowed due to a q value of 0 then the handler will set the response code 406 (Not Acceptable) and return.
@author Stuart Douglas