This example demonstrates the use of the ODL (Object Description
Language) parser module in scikits.rsformats.  The sample file
provided comes from the ASTER satellite instrument (see the aster
example's README for more information).  It returns a
dictionary-of-dictionaries, where the keys are either group names or
object names.  The value of an object name is a dictionary containing
its attributes.  The value of a group name is a dictionary containing
its objects or subgroups.

Note that the parser in scikits.rsformats is not perfect; while it
supports all commonly-used aspects of the ODL language, more esoteric
aspects (such as arbitrary bases) are not supported.  Also, a
BEGIN_GROUP can be closed by an END_OBJECT, and vice versa.

TODO: update parser to support full specifications of ODL language.
TODO: example switching between text files of ODL and HDF files.
