Support returning arbitrary HTTP status codes

[SteveSandersonMS]

Currently, Sat is limited to returning status 200 for all successful responses. You can only set custom status codes for error responses. I'm not sure what even happens if you want to send something like a 301 redirect - is that a success or an error response?

To generalise this to host arbitrary web endpoints, it would be ideal if developers could set any HTTP status code they want, independently of whether the response is being signalled as an error or not.

[cohix]

Oops! I meant to link your other issue... this will be addressed in a future version, though :)