Add support for config directories

[scottbreyfogle]

I'm currently running into a problem where I'm maintaining config files, but I don't have full control over the location where they live. Under different running conditions, they are in different locations. I'd like to be able to specify the directory relative to which config files should be loaded.

Note: when I try to run tests on this code, I get 4 test failures. But I get the same error when running at main.