Add benchmarks

[vil1]

We need a benchmarks sbt module with benchmarks for the functors produced by all our interpreters.

As satisfying first iteration would:

• define a "meaningful" example schema (complex enough to contain at least one instance of every members of the Schema ADT).
• for each interpreter, provide an "honest" implementation of the same functor, as it would be implemented "by hand" in real-life. For example, implement a play.api.libs.json.Reads using the Json.reads macro.
• compare performances of both the derived and the manually implemented functor to come up with a performance score.

[plokhotnyuk]

Please, do not use the most inefficient JSON library for growing a new one... It will be too hard to spot any changes in performance and allocation rate with it.

Let's compare with one of the fastest, like jsoniter-scala which already has a quite efficient derivation by a macro that is on par with the manual one in runtime.

[vil1]

I think your comment would be more relevant to #32, see you there ;)