Change BuildType to Package
Revise .gitignore
Use ggmap to plot station locations

Revised code to use the 'get_map' function in the
'ggmap' package for overlaying locations of surface
met stations.
Create function 'plot.calmet.domain'

Wraps the plotting code into a function with no
arguments for the time being.
Change required packages, refine ggmap code

Reduced the number of require statements to those
necessary. Changed the ggmap code to load in the
stations CSV file where necessary to avoid creating
the stations data frame object.