Set origin to zero

[AliciaSchep]

Especially for bar charts, I often want to set the bottom of a plot to zero. This is now fairly easy thanks to tidyverse/ggplot2#1805

ggplot(mtcars) +
  geom_bar(aes(x = factor(cyl))) +
  scale_y_continuous(expand = c(0, 0, 0.1, 0))

For a chart where data doesn't automatically go to zero, you also need something like limits = c(0,NA)

I'm not exactly sure yet what the best form of a helper here is, will think and update, but wanted to get the ball rolling with issues for possible helpers.

[AliciaSchep]

Thinking about this a bit more, I think what might be helpful is something like easy_exact_ylim which is like ylim but also sets expand to 0 for any non-NA bound, so that the limits you set are exactly the limits of the plots.