an incremental step toward better converters

this is a step toward a better converter system for configman.  The immediate benefit to this change is that the excessive quoting done by the ini handler is gone and paths to classes are completely qualified.

Some redundancy has been eliminated (there was more than one timedelta converter), and the converter section has been arranged into three sections: utility, from string and to string


It should even work to do:
```python
self.assertEqual('"configman.tests.test_converters.Foo'", Foo)
```