Documented series chart
Added several tests for series chart, fixed subchart delegation bug.

_preprocessData needs to happen before _generateG in coordinateChart,
otherwise series chart options are not applied to subcharts
(for instance, transitionDuration, which needs to be 0 for tests).
Added series chart tests for seriesSort option
Add more direct unit tests for renderDataPoints and dotRadius.
Merge pull request #378
readded case in renderDataPoints for falsey arguments and added tests
Note that we cannot test transitions with jsdom
Merge pull request #380
pull request line dashStyle
Fixed crash when all stackableChart stacks are hidden
fix to dots color on line chart
Fixing bug around title of LineChart stacks being incorrect when other stacks are hidden
Adding hidableStacks as an option for stackableChart to hide/show stacks.
Greying out legend labels on hiding stacks.
Fixing bug around color of stack dots not being the same as color of the chart when other stacks are hidden
Removed extraneous spaces in title documentation
Fixed bug where BarChart stacks did not have individual titles
Documented hidableStacks
Hovering over hidden legend items should not fade out other stacks
some optimization for computeOrderedGroups