an example to evaluate and echo different R code; should close yihui/knitr#383 now
for the `document` hook, x is not necessarily a scalar now; for this example, need to paste() by \n
a blank line disappeared because knit() does not include an \n in the last line now

https://github.com/yihui/knitr/commit/0f69a24114ff374bbab4a8e2ec078bc22c29a99e
forgot to put `;` after each line of command
make, and the big5 example was knitted