Optional height and width. Added window resize redraw.

Made height and width optional. If missing, the height or width will
be taken from the parent element.

Added a window resize hook to redraw graph. Combined with the parent
element dimensions, we can now make responsive graphs possible.
Merge branch 'master' of https://github.com/patrickrs/angularjs-nvd3-directives into patrickrs-master

Conflicts:
	dist/angularjs-nvd3-directives.js
Added additional examples to test automatic resize