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

# Roundup requires Python 2.7+ as mentioned in doc\installation.txt
from __future__ import print_function
import sys

VERSION_NEEDED = (2, 7)

if sys.version_info < VERSION_NEEDED:
    print("Content-Type: text/plain\n")
    print("Roundup requires Python %s.%s or newer." % VERSION_NEEDED)
    sys.exit(0)