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


I guess it adds a certain value of simplicity in that you can just import straight from converters.py instead of doing any optimization wrapping yourself in the external package (e.g. crontabber).