Expose functionality as a library

[stathissideris]

This is a useful project and I think it would benefit the Clojure community if we had access to it as a library. In order to do this you could take the following steps:

1. Explain in the readme which function(s) from which namespace a developer should call in order to render a sequence diagram
2. Explain in the readme what the expected input of the function in question looks like. I know that there is already a DSL which is used as input when the diagram is generated based on a file, but Clojure devs would find it useful to be able to pass a data structure instead of a file/string as input, so this part of the documentation should explain what this data strucure looks like.
3. Add a deps.edn file in addition to `project.clj. This will allow other Clojure projects to include documan as a library based on git URLs without you having to publish it manually. Read this guide on how to do it: https://clojure.org/guides/deps_and_cli
4. For Leiningen users, you can publish documan to the Clojars repo, see https://github.com/clojars/clojars-web/wiki/Pushing

I hope that's clear enough!