Log Message:
(devel/R-evaluate) Updated 0.15 to 0.19

Version 0.19
================================================================================

- In `evaluate()`, `keep_message` and `keep_warning` will completely
  drop messages and warnings, respectively, when their values are
  `FALSE`. Previously messages would still be emitted (to the console)
  even if they take `FALSE` values.

- Fixed the bug that `parse_all()` fails with line directives (thanks,
  @ArcadeAntics, #114).

Version 0.18
================================================================================

- Fixed tests that were still using the deprecated `ggplot2::qplot()`.

Version 0.17
================================================================================

- Adapted a unit test to the next version of **ggplot2** (thanks,
  @thomasp85, #113).

Version 0.16
================================================================================

- Fixed a bug that an empty **ggplot2** plot could be recorded and
  incorrectly saved (thanks, @sjspielman, rstudio/rmarkdown#2363).