Merge pull request #662 from jranke/master

Improve scrolling behaviour of gWidgetsWWW2 notebook example
need to filter the authors; the CRAN page is not correct: http://cran.r-project.org/web/packages/knitr/citation.html
use the `@include` tag to prepare the upcoming changes in roxygen2 (Collate will be gone)

klutometis/roxygen#139
expose the code option and make it possible to generate the code chunk programmatically
add AsciiDoc and Textile to the reference card, and use smaller fontsize for the table
bump version
the default device is NULL in opts_chunk, which will be changed to pdf for LaTeX output, and png/svg for HTML output

this allows one to opts_chunk$set(dev) before knit(); previously, if you set dev=pdf before knitting an Rmd document, the device will be restored to png forcibly, which is bad when we want to convert markdown to LaTeX through pandoc
factor out the code to crop images to plot_crop(); we can use it separately later
document and export plot_crop()
add a fig.process option to post-process plots
a helper function is_windows()
do not reinvent shell() under Windows
change tidy=TRUE to tidy=FALSE!
roxygenize
play fire with crandalf: https://github.com/wch/r-source/commit/08814645839
wrap up fig.process into fig_process(), and change the meaning of x in hook_plot_foo()

x is just the filename now; c(basename, ext) was largely for the convenience of LaTeX \includegraphics{}
be explicit in fig_path()
use the latest version of roxygen2, with no wrap and no indent
065 is a better example; asked again -- closes #667
bump version