- Split into `config/__init__.py` and `config/utils.py`

Split into `experiments/__init__.py`, `experiments/input.py`, `experiments/output.py`, and `experiments/utils.py`.

Split into `learner/__init__.py` and `learner/utils.py`.

Move all `utilities/*.py` into `utils/commadline/*.py`.
Move skll constants from all across codebase into `utils/constants.py`.
Move `logutils.py` into `utils/logging.py`.

- Remove unnecessary functions and classes from top-level namespace.
- Remove some unnecessary newlines.

- Add new sections for `config` and `utils` packages.
- Replace "module" with "Package" in various places.
- Remove documentation for functions that are no longer in top-level skll namespace.

- Call it `load_custom_learner()` and have it return the object instead of populating `globals()` directly.
- Populate globals() where this function is called instead,