Changes:
* utility functions in `hatlib` now make use of the HAT object model (OM). Previously, `tomlkit` was being using directly and was bypassing the checks and OM construction of child objects.
* `hatlib.load` now returns a `HATPackage` object that results from deserializing the HAT file passed in. Additionally, if functions can be loaded, a non-empty `AttributeDict` is returned as a second value.
* Moved test folder to be a sibling of library folder. Now the package no longer contains the tests when installed. Additionally, the library can be tested by running `python -m unittest discover test` in the root of the repository.
* Adds YAPF style config to setup.cfg and formatted all touched files with `yapf`
Kern Handa