Added module doc string

Imported POSException

Parameterized MAXTEMPFSIZE

Added exception classes

Added docstring to _dbnames explaining what each database is.

Made all struct.pack and struct.unpack calls which deal with integers use signed integer representations.

Added exception handling for out of temp space.

Added workaround for import which defers adding a new object to the "zeroes" directory "out of the gate".  This fixes import (it was broken).

Added a pack method.