Fix bad documentation.

Don't mislead in the documentation.  When reading 24 bytes, 24 bytes are read.
Not 16.
Make sure fields names are properly set.

Due to the way MATLAB stores field names for structures, individual items
in the structure don't have names.  Thus, one must use the field name.  Fix
the grab bag parsing to do this correctly, and add a test to verify correct
behaviour.
Start reading more property related fields.

To support multiple objects with differing field values for the same class
type, it is now necessary to actually parse segment 4 and act accordingly.
Thus do that, and add a test to ensure the behaviour is correct.