Refactor so represent and outcome can be removed from requirements

[skewty]

I see each of them is used for exactly one line of code each. Might you be willing to write a bit more code to do away with them?

setup.py

requires = [
    'represent>=1.4',
    'sqlalchemy',
    'outcome',
]

Or, alternately, would you be open to a pull request that did this?