Adding parameter features

Added additional operator called "in" which constrains a parameter to be within a List of values.
Currently only works for List[Int], Range, and List[Chisel.IntEx].
Example uses:
  params.constrain(ex => ex[Int]("this") in List(1,2,3,4))
  params.constrain(ex => ex[Int]("this") in Range(1,5))
  params.constrain(ex => ex[Int]("this") in List(ExLit(1),ex[Int]("that")))