FIxing bug in line.js.
Merge branch 'master' of https://github.com/novus/nvd3

Conflicts:
	nv.d3.min.js
Adding historical bar chart code.
Merge branch 'master' of https://github.com/novus/nvd3

Conflicts:
	examples/historicalBarChart.html
	nv.d3.js
	nv.d3.min.js
	src/models/historicalBarChart.js
	src/nv.d3.css
Adding PNG image to show what a sample line chart looks like. For the WIKI documentation.