Merge pull request: dataset slopeAndAspect return object, not array
Util: Hybred arrays, Data: use hybred arrays for slopeAndAspect()
	- util: aToObj(array,names) adds named properties to array in order of array indices
	- Data: slopeAndArray returns hybred array: {slope,aspect,dzdx,dzdy}
	- Dropplet: see dropplet model for example syntax variations.
Merge branch 'master' into gh-pages