Move dictionary for string types out of SoundFile class
Remove superfluous parentheses in return statement
Fix __setattr__()

In new-style classes the base class __setattr__() has to be called
instead of inserting the value into self.__dict__.

See http://docs.python.org/2/reference/datamodel.html#customizing-attribute-access
Fix a seek-related bug
Read whole file if frames is negative

... in contrast to if frames == -1

This corresponds to the behaviour of standard Python file objects.
Add close() method

Closes #14
Return float64 by default

Closes #17
Fix missing 'count' in vio_write()
Add _getAttributeNames()

This is useful for auto-completion in IDEs.
Make __getattr__() more compact
Remove exclamation marks from error messages
WIP the rest