Macro generated case class Tuple Setter and Converter

This is a first stab at using macros to begin generating useful code for our users.

Caveats:
* this only works on 2.10. I play around with it by doing: ```./sbt ++2.10.4 "scalding-macro/console"```
* this depends on macro paradise. I do this for quasiquotes, which GREATLY simplify the implementation... it isn't strictly necessary, but would greatly complicate things. quasiquotes are part of scala 2.11 so depending on macro paradise only for them seems ok to me.
* I need to add tests, though I've tested it along the way of course.

What are other things we might want to use macros for?
The macro-provided implicit will hide the implicit value in the companion object in implicit search, just as if you'd imported any other old method providing an implicit value of the same type. You definitely could have the macro check for an existing implicit value with `c.inferImplicitValue(weakTypeOf[Foo[T]])`, though, and pass that through if it exists.