wrap=FALSE is the default for roxygen2 4.0, and @S3method has been deprecated
more changes from roxygen2 4.0
for some reason, test_dir() does not signal errors when I used the test expect_true(FALSE); this might be a bug of testthat, but it seems we are supposed to use test_check() now
fixes yihui/knitr#722: clean up the last_plot object after each evaluate() call
bump version
prepare a CRAN release