Enhancement: Map rotation and North orientation badge. Fixes #178

[juandesant]

This change request provides three additional arguments to create_map_poster.py:

• Adds --offset-orientation/-O arguments to provide a rotation from north (positive is towards the east) in decimal degrees.
• Adds --show-north/--hide-north options which are complementary. When orientation is not changed (the default is zero), the default for this option is --hide-north, but still you can use --show-north to force the appearance of the orientation badge. Conversely, if there is a non-zero argument to --offset-orientation/-O, the default is for --show-north, but can be hidden with --hide-north.
• Adds a compass.svg file, based on a wikimedia commons file. The comments acknowledge the origin as per its CC-BY-SA license.

Please note that, in order not to introduce new dependencies, the SVG file is imported as a matplotlib Poligon, and uses the existing textures. More details on ROTATION.md.

[zkornbluth]

Played around with this for a bit, and it appears to be losing the parks and water layers for rotated maps.

Example:
python create_map_poster.py -c "Montréal" -C "Canada" -t ocean -lat 45.5009388 -long -73.681061 -d 35000

python create_map_poster.py -c "Montréal" -C "Canada" -t ocean -lat 45.5009388 -long -73.681061 -d 35000 -O -45