refs #1: added tests for making sure exceptions are being raised and fall back is being used.
refs #1: added custom exceptions
refs #1: refactor, used custom exceptions
refs #1: removed MissingConverter, created a fall back in stead
Merge branch 'master' into issue_1
Revert "backward compatibility for the win."

This reverts commit e1e209454e6efe35eb5552239266b963c3fc9b90.
refs #1: dropped support for python 2.5
refs #1: put in dummy converters in the test
refs #1: name change
refs #1: made changes based on review notes
refs #1: added a docstring
Merge branch 'issue_1' into issue_2