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.

try:
    from html import escape as html_escape_  # python 3

    def html_escape(str, quote=False):
        # html_escape under python 3 sets quote to true by default
        # make it python 2 compatible
        return html_escape_(str, quote=quote)
except ImportError:
    # python 2 fallback
    from cgi import escape as html_escape  # noqa: F401