Add ability to turn off file writing

Replacing the file name after --geojson or --kml with "no" will stop the
output from being written, this also works when using the config file.

For example, this will only output the .kml file:
    archmap.py --geojson no
Default to /tmp if config file is not present

If archmap.py is not supplied with a config file, default to using /tmp
for input/output locations.
Var rename: geo_output=geojson, geo_output_kml=kml

This renames 'geo_output' to 'geojson' and 'geo_output_kml' to 'kml',
no functional change, just makes it easier to read.
Update help and comments about output disabling