Use io.aviso.exception as the preferred way to print exceptions

The [io.aviso.pretty](https://github.com/AvisoNovate/pretty) library has a great exception printer. I've been using it with cider for a few days and it just makes reading exceptions a lot easier. 

The problem with my below implementation is that it requires that the io.aviso/pretty library is included in the project's dependencies. Is there any way to dynamically depend on the library using nrepl itself?

It might also be worth including a way for users to set their preferred exception printing method by creating a new option such as `cider-preferred-stack-trace-printer`. I'd be happy to add this too if you think it's a better approach.

![screen shot 2013-11-23 at 10 35 41 am](https://f.cloud.github.com/assets/495730/1607085/21fd0516-546e-11e3-9e37-cc8ce265c4ed.png)