more rstudio options
factor out the code to configure port and launch.browser to the config() function
when tools:rstudio is not in search path, see if the environment variable RSTUDIO exists; if it does, use rstudio::viewer()
mention the rstudio viewer
add jekyll() to serve Jekyll sites; rmdv1() and rmdv2() to serve R Markdown files

closes yihui/knitr#205
this package has a little more usefulness than before, so update its description
roxygenize
use xran/r-config, and deploy to xran after success
add a news item, update readme, and bump version