[#116] improve bar chart handling of mixed positive and negative values
[#116] improve line chart handling of mixed positive and negative values
[#116] implement line chart handling of mixed positive and negative values with stacking
upgrade d3 to v3 and fix some broken test cases
upgrade d3 from v2 to v3
Merge branch 'gh-pages-dev' into gh-pages

Conflicts:
	crime/index.html
	index.html
	js/d3.js
	js/dc.js
	vc/index.html
cache x unit count and improve example page focus performance