Pass ex-info in/out pods

Hi boot-ers!

Often, when working with tasks or pods that need to exchange info, we all have the restriction on the data we can send.

Fortunately @Deraen has already [thought about this](https://github.com/adzerk-oss/boot-cljs/blob/master/src/adzerk/boot_cljs/util.clj#L59) and it might make sense to actually include the two functions in `boot.util` as standard way for accomplishing this task (if I am not mistaken there are tests as well).

I can take care of this, also because I will need it in my other patch for `boot-reload`.

How does it sound?

Btw thanks for working on `boot`!