Produce setup using our usual patterns

- This is a bit of prep before properly kicking off [#71565298](https://www.pivotaltracker.com/story/show/71565298)
- We seem to do quite a lot of reading from other places to describe our package, hopefully these are some sensible methods for generating that setup description
- bounces the requirements to requirements files and then reads from there, keeping our usual pattern
- Reads the version from init, which is where I'd guess we're expecting the version to be
- I've shifted the `long_description` to it's own method within the Setup class, so as to protect its entirely fragile ego (only joking `long_description`, I know you're good! As if you'd be bothered about something as trivial as instance invocation. Let's go grab a couple of brews, kick back and talk about the good old days when `HERE` was still doing the rounds.)