* cgi: return error page if 0/0 coordinate was used

  0/0 (wgs84) is almost always indicating an error, especially if bicycle
  routing is requested (this coordinate is in the Atlantic).

  For output_as=json, the error page is returned as json, otherwise
  it's simply a text/plain response.

  With test cases in cgi-test.t
* cgi: send_error logs to stderr/error_log
* data update