Updated CompositeSpace's np_format_as and _format methods to support formatting to other CompositeSpaces with identical tree structures.

Also updated VectorSpace's _format so that it returns the batch unchanged when formatting to an identical VectorSpace (it used to throw an exception).
pep8 cleanup
Added docstring to CompositeSpace's np_format_as and _format_as
Merge pull request #476 from SuperElectric/updated_format_as

Updated CompositeSpace's np_format_as, _format_as to support formatting to another CompositeSpace.