feat: paths now define a distance between them

feat: paths now define a distance between them

When you travel from town to town, the distance is defined the in asset
spreadsheet. The actual distance you travel is between 3-10% of the
total distance applied as min/max bounds.

At 50% of the distance between two towns the background image will
change to denote that you are approaching that town. At this point the
monsters you start to encounter will be ones tied to the destination town.