Add 2 arguments to websockify.WSRequestHandler for security

[rohitkode]

For additional security, it would be good to add 2 arguments to websockify.WSRequestHandler as follows:

• file_only: To disable directory listing, if set, return 404 response if non-file contents
  are requested.
• no_parent: To disable directory traversal return 403 response if contents
  out of the web root are requested.

This would enhance an additional layer of security to the web requests.
A patch is welcome, or I can submit one.

[DirectXMan12]

The pull request about should fix this issue (the autoclose syntax was just a bit off, though)

[astrand]

The file_only argument makes sense. However, I don't understand the logic or purpose of no_parent. First of all, when is it ever useful to allow returning files outside the web root? I believe this should never be allowed, thus "no_parent" should be default. Also, as far as I can tell, this was already the case: I don't see how it was ever possible to retrieve files outside the web root. We are using SimpleHTTPRequestHandler and its translate_path function (which sets .path) filters out ".." etc.