Add basic CORS support

[mathieuancelin]

This PR add basic support for CORS mechanism.

can be used through the programmatic API

server.configure(routes -> routes.
  options("/mycorsservice", context -> {
    if (context.isPreflight()) ...
    return new Payload("")
      .withCode(200)
      .withAllowOrigin("*")
      .withAllowCredentials(true)
      .withExposeHeaders("X-WHATEVER")
      .withMaxAge(3600);
  })
);

or the annotation based API

public static class MyResource {
  @Options("/mycorsservice")
  @AllowOrigin("http://www.code-story.net")
  @AllowMethods({"GET", "POST"})
  @AllowHeaders("X-WHATEVER")
  public String myService() {
    return "";
  }
}

[dgageot]

Related to #32

[jeanlaurent]

Closing since #32 is closed.

Thx a lot Mathieu

[dgageot]

?? Why did you close it? I didn't want to merge it right now but stil...

[jeanlaurent]

my bad

[cexbrayat]

Would be great to have this PR merged!

[dgageot]

PR merged