Make println statements configurable

[sveri]

Hi,

I am using joplin and also do so in my integration tests. The problem with this is, that the console is cluttered with joplins println statements and it is hard to find any meaningful error inbetween.
It would be nice if I could configure them, just like I do with standard java logging libraries.

[martintrojer]

I suggest wrapping joplin calls like this;

(log/info 
  (with-out-str
    (repl/migrate conf .. ..))

Also discussed #60