Initial support for the Cross-Origin Resource Sharing specification.
This allows JavaScript to make requests across domain boundaries.
Also reviewed the filter example to get rid of the context and
the generic classes (we can actually use {WSF_REQUEST}.execution_variable
and {WSF_REQUEST}.set_execution_variable).
Links:
* How to enable server-side: http://enable-cors.org/server.html
* Specification: http://www.w3.org/TR/cors/
* Github: http://developer.github.com/v3/#cross-origin-resource-sharing
Filters are part of a filter chain, thus following the chain of responsability
design pattern.
More information are available in library/server/wsf/src/filter/README.md
