Allow custom renderers

args.renderer can be a function that generates a custom Renderer.
Renderers should inherit from Rickshaw.Graph.Renderer and must have the
`name` property.
Merge pull request #253 from chrisirhc/feature/allow-custom-renderers

Allow custom renderers for Rickshaw.Graph
Scaled series, adapting hover detail for scaled series, adding a scaled Y axis, updated examples
rename Rickshaw.Graph.Axis.Scaled to Rickshaw.Graph.Axis.Y.Scaled
use supplied index vars instead of doing on our own
fix up doctype on scale examples
update built libs for version 1.3.0
Multiple normalized series causes "seriesData.forEach not defined"-Exception

Because seriesData is null at this point. The data does contain less elements than this.series. 
btw: Iterating over an array with the index of another array seems dangerous to me. So my quick fix won't be the best one anyway.

Example code can be found here: https://github.com/unSinn/plant-vertx/blob/master/webroot/js/plant.js
Merge pull request #258 from unSinn/patch-1

Multiple normalized series causes "seriesData.forEach not defined"-Excep...
add back using our own index iterating through series
add multi renderer to combine different renderers on one graph
add minimal error checking around series renderers in multi renderer
Added instructions on how to run the tests.
Delayed validation in Rickshaw.Graph.Renderer.Multi

While I'm really quite fond of validation and performing it early to ensure that any constraint violations fail fast, unfortunately the check for all the series having a renderer if the graph 'multi' renderer is used cannot be performed in the initialize of the renderer as all graphs will create an instance of the renderer even if it isn't used.  This can be seen by performing:

make clean build

and then npm test
Merge pull request #261 from rojotek/patch-1

Added instructions on how to run the tests.
Merge pull request #262 from rojotek/patch-2

Delayed validation in Rickshaw.Graph.Renderer.Multi
Update README.md