MapQuest Open tilesets

Add support for MapQuest Open (alternative OpenStreetMap rendering) and
MapQuest Open (public domain satellite imagery) tile sets
Allow rendering w/ custom template

New argument to create_map(), template, lets you pass a string to use
as template for output.
Merge pull request #4 from samatjain/openmapquest

MapQuest Open tilesets
Merge pull request #5 from samatjain/customtemplate

Allow rendering w/ custom template