Support for 'geom_histogram()'

[trevorld]

• There is no geom_histogram_pattern() but ggplot2::geom_histogram() supports filling histogram bars with "stacked" fill colors. Not clear to me why we shouldn't include a geom_histogram_pattern() for completeness sake:

  ggplot(diamonds, aes(price, fill = cut)) +
    geom_histogram(binwidth = 500)

  

• If we do this then geom_bar_pattern() should call geom_histogram_pattern() instead of geom_histogram() if accidentally fed a binwidth parameter.