Conditions in Term#valid_datatype? rewritten to test explicity for boolean classes.
Fixes #39
Prepping release 0.2.3
Merge pull request #40 from dchandekstark/39-valid-datatype-fix

Conditions in Term#valid_datatype? rewritten to test explicity for boolean classes.
Fix incorrect exception syntax

Closes #36.
Get rid of the singleton_class stuff. Create a builder object for creating the accessor methods