Suggestion: Add-in to run examples

[pbreheny]

Just a suggestion, but I think it would be nice to offer an Rstudio add-in that allows the user to check all examples for a package with a keyboard shortcut. In other words, add this block to inst/rstudio/addins.dcf:

Name: Run examples
Description: Runs R code in examples using `devtools::run_examples()`
Binding: run_examples
Interactive: true

[jimhester]

Sure, do you want to create a pull request to add this?

It would basically be what you have above plus a note in NEWS.md mentioning the new add-in