maptracker

### FORKED FROM: https://gist.github.com/cavedave/8ff22e94c882e9f6be933f99f2ae0b50
## Charles changed:
##   Absolute URLs to library/data (rather than local files)
##   Raster rather than tiles (didn't like the grid lines)
##   Gradient from red (hot) to blue (cold) with black at zero (no change from average)
##   Removed year filter
##   Defined title and breaks via automatic extraction of dates from data
##   Scaled down plot to be more friendly for Gist
##   Took out unused libraries