Added a TypeError exception if a value going through the marshaler is not a marshalable value such as an empty string, or an unknown class instance.
Added an empty check to the marshalString command.
Added a TypeError when none of the unmarshaling commands can handle the
type. This shouldn't really ever happen unless you're doing something
really strange like using the unmarshal function on a non dynamodb
object.
Cleaning consistency of single and double quotation marks.
consistency across wording in tests.
Merge pull request #3 from nackjicholson/ISSUE-2

Issue-2