Added module synopsis for the chapter summary.

Added module synopsis for the chapter summary.

Added documentation for TestCase.assertRaises().

Added text for "Mapping concepts to classes", and merged it into the
front matter instead of separating it into a new section.

Removed use of "assert" in examples.

Update the descriptions to reflect further changes from discussions on
the pyunit-interest list.

Added documentation for the defaultTestLoader object and the
TestLoader methods.

Added the assert*() names for the TestCase helper methods.