PARTIAL: Add support for data attribute overriding
Implement customizable getters
Move `getters` definition to Chart initialization

Only the consumer should be defining getters, so a method on the Chart
instance is overly powerful.
Simplify dataAttrs API
Temp
I think this is right.
Fix tests
Remove declarative getter API
Refactor and remove `Chart#translate`

I'm not sure we need an explicit method to toggle the translation
operation...
Remove custom Errors

This was the wrong way to implement this, anyway.
Name virtual attributes appropriately

It's a bit confusing to use the term "data attribute" for two distinct
concepts.
Update API naming for clarity
Implement inheritance of data attributes
Optimize data attribute inheritance
Remove unused statement
Add test for primitive data types
PARTIAL: Begin IE8 support