[WIP] Scala 2.12 (help needed)

[thomastoye]

See also #71

I did some preliminary work to make couchdb-scala work with Scala 2.12 (selecting and upgrading to dependencies that are 2.11 and 2.12-compatible). It compiles, but the tests don't pass yet. I get the following message when running test and then sbt locks up:

Exception in thread "http4s-blaze-client-2" java.lang.NoSuchMethodError: scalaz.syntax.Syntaxes$either$.ToEitherOps(Ljava/lang/Object;)Lscalaz/syntax/EitherOps;
	at org.http4s.util.TaskFunctions.$anonfun$futureToTask$2(Task.scala:26)
	at org.http4s.util.TaskFunctions.$anonfun$futureToTask$2$adapted(Task.scala:25)
	at scala.concurrent.impl.CallbackRunnable.run(Promise.scala:60)
	at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1142)
	at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:617)
	at java.lang.Thread.run(Thread.java:748)

I fear I may have accidentally included incompatible dependencies. Anyway, I would appreciate it if someone could take a look a this and possibly finish this - I don't have a lot of time for this ATM.