Enforcing black

[kazamatzuri]

As discussed in #60 adding pre-commit config for black.
You will need to have pre-commit installed on your environment for this to work (and black).

(this is gonna be easier to merge once #59 is through )

[RookieRick]

Am I correct in my understanding that this PR is superseded by #68 and should just be closed now?
Have tested after merging 68 and confirmed that:

1. If a developer follows the instructions and installs pre-commit script, Git and black will do their thing when they try to commit, and
2. If a dev doesn't install pre-commit script, Travis-CI will fail PR if black test fails.
   Huzzah!

[juliusiv]

@RookieRick yep, this can be closed now. Thanks @kazamatzuri for getting this started!