Improve plotting method

[mitchelloharawild]

Currently the plotting method simply shows equally spaced points on the pdf/cdf. For many distributions this is insufficient - the spacing should be concentrated on positions of change.

The example below shows a zero-inflated normal, however the zero is not shown due to the equal spacing.

MRE:

library(distributional)
library(ggplot2)
autoplot(distributional:::dist_inflated(dist_normal(), 0.5))

^{Created on 2020-01-21 by the reprex package (v0.3.0)}

[mitchelloharawild]

Note the CDF:

library(distributional)
library(ggplot2)
autoplot(distributional:::dist_inflated(dist_normal(), 0.5), "cdf")

^{Created on 2020-01-21 by the reprex package (v0.3.0)}

[mitchelloharawild]

Graphics will be handled by the {ggdist} package.