from alchemy.begin return the alchemy object so that it can be aliased

[hdngr]

for example:

var viz1 = alchemy.begin(someConf);
var viz2 = alchemy.begin(someOtherConf);

viz1allNodes = viz1.get.allNodes()
viz2allNodes = viz2.get.allNodes()

// etc....

[ghost]

Just commenting for later reference before a commit takes care of this: while returning the object is just a one liner, we need to make sure that when there are multiple instances there is no bleed in operation, either through API (which there shouldn't be) or through user interaction (more likely due to d3.selectAll(), though hopefully not a problem.)