if we set the chunk option dev.args = list(useDingbats = FALSE), it may be passed to other devices such as png; see comments under 1029bd9

knitr 1.5.31 makes it possible to set device arguments for a single device using a named list
reduce height of iframes in ioslides
Merge branch 'master' of github.com:rstudio/rmarkdown
bump version
tweak iframe sizing in ioslides
only run pandoc-citeproc if a bibliography field is specified
URL-decode path information in Shiny Run Document case
emit relative rather than OS-specific path in HTML (when not self-contained)
Merge remote-tracking branch 'origin/master' into feature/shiny-dependencies