Cross-Origin Resource Sharing initial support

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
CORS: respect specification regarding Access-Control-Allow-Headers

According to the specification, the value of the response header
Access-Control-Allow-Headers must contain at least all the values of the
request header Access-Control-Request-Headers to be considered a valid request.
Before this commit, only the Authorization value was present, which is enough
for Firefox but not for Chrome.
This should now work as expected.
Merge remote-tracking branch 'jocelyn/flexible_response' into cors

Conflicts:
	examples/filter/filter-safe.ecf
	examples/filter/src/filter_server.e
	library/network/protocol/http/src/http_header.e
	library/server/wsf/src/wsf_response.e
Use new upstrem method put_header_key_values
Filter example: remove unused libraries in ecf file
Use features from the flexible_response branch
Fix indentation
Merge branch 'cors' of github.com:oligot/EWF into cors
Merge remote-tracking branch 'upstream/master' into cors
Merge pull request #22 from oligot/cors

Cross-Origin Resource Sharing initial support