initial grunts file to run regression tests

originally done in a shell script
discard stdout for pdfgen because it causes grunt to fall over
remove genhtml dependency
add option to generate CSS coverage info
add compile task that generates CSS for all books
simplify task names
add error checking to make sure prereq files exist
better error handling when prereq file is missing
add color when skipping and add task descriptions
show the number of differences found for each book
update TODO and example config file
add prereq checking
make the prepare and diff tasks support a single book
add instructions for using grunt
modify coffee file to allow VERSION to tested without .xsl extenstion as it exists in docbook directory
run grunt diff for npm test
added smarter skip config and preview HTML
Merge pull request #191 from Connexions/gruntjs

Add support for regression testing and building using gruntjs