Added support for RequireJS AMD.
Merge branch 'master' into merge526

Conflicts:
	dc.min.js
	dc.min.js.map
add amd support

based on PR #526 (thanks @spacelis!)
but without any pollution, as implemented in d3 here:
https://github.com/mbostock/d3/commit/99ff885b960309f03ca5142ada3fcfe1a56f8604
Merge pull request #590
bump stable version