Minor spelling changes, whitespace removal, and improvement to Snap.set() API
Minor spelling changes, whitespace removal, and improvement to Snap.set() API

This commit includes ensuring methods exposed by the Set API is typed in a
consistent manner as per documentation:

* `.attr()` always returns `Snap.set`
* `.getBBox()`, `.insertAfter()` is added

dsebastien/DefinitelyTyped,borisyankov/DefinitelyTyped,magny/DefinitelyTyped,georgemarshall/DefinitelyTyped,mcliment/DefinitelyTyped,magny/DefinitelyTyped,markogresak/DefinitelyTyped,georgemarshall/DefinitelyTyped,georgemarshall/DefinitelyTyped,borisyankov/DefinitelyTyped,dsebastien/DefinitelyTyped,georgemarshall/DefinitelyTyped