Move deps off the project, fixes #2

[arichiardi]

As per title, fixes #2

[gja]

Thank you for the pull request. Let me think about this a bit. Even if it is a runtime dependency, I wanted to add log4j in the deps, so that this is the only library one needs to add to their project. Let me think about alternate ways to do this

[arichiardi]

@gja of course! 😄 also consider that you don't always want your transitive deps to interfere with each other and 90% of the time you will need to specify a top level dependency to disambiguate the version that maven pulls in. What I mean is, if all your libs that use log4j pull different versions of it, who wins?

If you leave this to leiningen if I remember correctly the transitive dep closer to the vector top (meaning...smaller index) will win, but you'd better have control on that 😄

In any case, thanks for answering so promptly, I'd really love to see a log4j2 clojure lib shining. Log4j2 has unique features (context, async loggers, ...) and it is a pity that clojure.logging does not include it atm.