Convert Rd to roxygen documentation

	* use Rd2roxygen('path/to/your/package') to update 
		the R scripts under ./R directory
	* other functions might be useful for individual files
		* parse_file
		* create_roxygen
		* parse_and_save

Utilities to run roxygen and enhance documentation

	* roxygen_and_build() (or rab() for short) will run roxygen2
          and try to reformat the examples code in the documentation
          using the formatR package

Originally written by Hadley Wickham; improved by Yihui Xie
