Create function toFill()
Default ggplot color for geom_area and geom_ribbon
Default line color for geom_area and geom_ribbon: NA
Re-ran roxygenise() with new roxygen2 version
Change 'color' to 'colour'
Increment version number to 0.5.7
Merge pull request #137 from ropensci/pedro-ggplot-colours

ggplot: geom_area and geom_ribbon: fill and line colors