Rendering changes and improvements

Draw at double the requested size, then scale down with a light blur
Plot single pixels instead of circles - gives a much better result
Use a transparent background instead of black
Composite "Over" instead of "Multiply" - leaves the map 100% visible
TODO Investigate a light gray overlay to slightly dim the map
Easier way of limiting the map bounds without having to trim the data

New option --bound picks a bounding box from a predefined list
Calculated zoom can be overridden with "--bound name@12" (for zoom 12)
Allow the auto-calculated zoom to be overridden

Specify --zoom with --auto to have the bounds auto-calculated but use a specific zoom
Add Open Static tiles from Mapquest as an alternate source

Mapquest Open Static images çan be bigger than 640x640, skip the check in this case
Add a new option (--[no]map, identical to current --[no]gmap) to disable map tile fetch+composite

TODO revisit this for refactoring - use a list of tile providers instead of A|B choice, etc.
Fix silly issue where using --auto always forced zoom to be 7
Rogue brackets ruined my afternoon
New option --fade to dim the map tiles before compositing

Helps with the (busier than GMaps) Mapquest tiles.
Merge branch 'osm-statics'
Merge branch 'faded-map-tiles'