Remove @Override to allow build with Java 1.5
Updated documentation and xsd to fix build

  - nsa-add-headers children are not alphabetically sorted
  - nsa-add-headers reference in children of http should be in alphabetical order (it was last and the documentation exects each child element to be alphabetical)
  - The id nsa-add-headers-parents was not expected since it was not specified as a child of <http> in the xsd.
  - The id nsa-xss-protection-enable was not expected because was missing a "d".
  - The following ids were expected to be documented, but were not [nsa-xss-protection-enabled, nsa-xss-protection-parents, nsa-frame-options-parents, nsa-content-type-options-parents, nsa-header-parents]

I also moved the documentation in appendix-namespace.xsd to be "flat" like the other documentation. For example, the nsa-add-headers section is not a child of nsa-http. The reason for this is otherwise the font gets too small in the manual.
Merge pull request #1 from rwinch/add-headers

Add headers