Fix 204 responses, hangs and crashes with REST. Remove Content-Type and make sure no content is returned by OPTIONS request in REST interface. In write_html set the Content-Length when response is not encoded/compressed (fixes hang due to missing content-length with unencoded data). In REST interface do not raise UsageError for invalid api version. Return json error with proper message. Fixes crash.

#!/usr/bin/env python
from __future__ import print_function
import zlib, base64, sys
print(base64.encodestring(zlib.compress(sys.stdin.read())))