Should the next version require ggplot >= 0.9.1

[briandk]

The proposal

If we require v0.9.1, we can eliminate our geom_rug_alt and just use a geom_rug() call with a sides argument.

From the 0.9.1 release notes:

• geom_rug now allows control over which sides to put the rug lines, with the sides argument. (Thanks to Winston Chang)

  Advantages

  1. Our codebase shrinks, because we don't need to maintain this code anymore; we can remove it all
  2. We remove questionable calls to ggplot2 that have to use a triple-colon notation
  3. We move away from proto-based geoms in general, which (I know, I know) ggplot2 is ultimately planning to do in the long run anyway
  4. The change is under the hood; it shouldn't break existing user code at all. They shouldn't notice any difference in how to call our functions.

     Disadvantages

  5. Users can't upgrade our package without being forced to upgrade ggplot2 first
  6. We'd need to verify first that we can achieve (reliably) the exact same visual effect with a sides argument as what we're getting with our custom geom. That shouldn't be hard, but we have to do due diligence. We can't just change and hope.

[briandk]

The verdict? Yes, we're requiring ggplot2 v0.92: 42c2aafbc497eeb868d89a09ed8b59cb3a539244