Fully tranverse dataset graphs with Dataset.select
DataView.from_stack can concatenate along existing dimensions, too
Added variable.T as shortcut for variable.transpose()
Added Variable.apply and DataView.apply
Revised and extended new README
Renamed "Variable" -> "Array" and "DataView" -> "DatasetArray"

I think these names are much more straightforward. The only annoying
aspect is that "array" is the name of a built-in module, which conflicts
with naming the module "Array" is in "array".