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?
I don't know if this is a big deal, but I'd be more comfortable doing something like this:

``` scala
val memberTypes = tag.tpe.declarations.collect {
  case m: MethodSymbol if m.isCaseAccessor => m.returnType
}
```

Which lets you use the nice `isCaseAccessor` information instead of relying on the way the case class magic generates a constructor for you.