Merge pull request #10 from AndreyAkinshin/master

A child example from http://yihui.name/knitr/demo/child/
mention out.width in slides as John Maindonald suggested
some changes in R 3.0.0
cache the pdfcrop example
remove xtable comments
use lower case *.rnw because I do not want to compile the child document individually
recompile all examples; changes are due to:

1. I moved upquote before \begin{document}
2. I set random seed for random numbers
3. I use input filename as the figure prefix
newlines at the end of files