add some y offset to particle
finish writing gravity and charge recipe
finished force momentum recipe
finish link constraint recipe
first draft of chapter 11
clean up
update readme
start tdd bar chart recipe
add width and height
add chart body
add data method
add bar creation
add bar width calculation
add x mapping
add bar y mapping
some minor adjustment of bar width
Merge branch 'master' of github.com:NickQiZhu/d3-cookbook
fix data loading issue