Fixed broken reference for "Custom Representations"
Added an example of filtering requests.

This particular one is for filtering requests that have omitted the "Date" header field.
Modified example filter to incorporate Jersey's ExtendedUriInfo
Added an example for writing and using ServletFilters.

The request follows the example used in the Jersey filter section.
Clarified Servlet Filter text, added reference to bundled filters
Cut away some boilerplate in filter example
Corrected filter registration example to a more idiomatic approach.
Merge pull request #553 from wonderb0lt/documentation-on-filters

Documentation on filters