Makes available for use outside the quantmod workflow a dataset
of appropriately transformed variables, using the same mechanism
underlying specifyModel. Offers the ability to apply transformations
to raw data using a common formula mechanism, without having to explicitly
merge different data objects.
Interally calls specifyModel followed by modelData, with the
returned object being coerced to the desired 'return.class' if possible,
otherwise returns a zoo object.
See getSymbols and specifyModel for more information
regarding proper usage.