Add tools to auto-format code to match the style guide

As mentioned in https://github.com/clojureverse/clojurians-log-app/pull/18#issuecomment-371048377

I think it will be very helpful to make use of
https://github.com/weavejester/cljfmt or
https://github.com/kkinnear/zprint
to help enforce the style guide.

It'd be even better to add a shared pre-commit git hook, to reformat changed files before they are committed. It might take a bit of effort to get the tools setup, but it'll be easy to keep the code style uniform.

It's just one less thing to have to actively think about when working on the project. =)

Start by reviewing the discussion in pull request 18 and comparing the proposed cljfmt and zprint tools. Define how formatting and a shared pre-commit hook should be configured for changed files; done means the chosen formatter is set up and the hook consistently enforces the style guide.

Written by the indexing model from the issue text.