Changes in dc.js version 3.0

Version 3 is compatible with D3 versions 3 and 4. Thanks to Deepak Kumar for all his effort on the port.

We've made every effort to keep the library backward compatible. Most of the changes you will need to make are due to the great namespace flattening of D3V4, documented in d3/CHANGES.md.

However in a few places the dc.js API or behavior has changed due to the upgrade. We also deprecated a few things, and you'll get browser console warnings unless you change your code.

We'll document those changes here. Since this is a wiki, feel free to add any changes we've missed!