List:
  slice(from: Int, to: Int): List[T]
  replace(from: T, to: T): List[T]
  chunks(s: Int): List[List[T]]
  zip[B](that: List[B]): List[(T, B)]
  -(e: T): List[T]
  --(that: List[T]): List[T]
  &(that: List[T]): List[T]
  pad(s: Int, e: T): List[T]
  find(e: T): Option[Int]
  lastOption: Option[T]
  firstOption: Option[T]
  unique: List[T]
  splitAt(e: T): List[List[T]]
  split(seps: List[T]): List[List[T]]
  count(e: T): Int
  evenSplit: (List[T], List[T])
  insertAt(pos: Int, l: List[T]): List[T]
  replaceAt(pos: Int, l: List[T]): List[T]
  rotate(s: Int): List[T]

ListOps:
  flatten[T](ls: List[List[T]]): List[T]

More info at https://z3.codeplex.com/workitem/113

- Ensurings/Require are now proper purescala trees
- Introduce Assert as a tree
- Simplify tactics to support arbitrary asserts/errors/inner ensurings
- New phase to inject assertions for unsafe calls (array/map access)
- Refactor Default and Induction tactic

- NormalizationRule becomes priorities, so that we can have multiple
  distinct layers

- Use the @library annotation, move synthesis stuff to synthesis,
  Oracles.

- Make sure tests use PreprocessingPhase and import synthesis when
  adequate

- Extract proper package objects fix patternRecons and simplifiers

- Reorganize library:
  - leon.{choose,???} -> leon.lang.synthesis
  - leon.{waypoint,epsilon} -> leon.lang.xlang

- Holes become chooses

- Unhandled types are removed, Untyped is now checked for and
  a warning is issued if an untyped expression is found.

This allows us to use them in synthesis. Expose --solvers=..
option for synthesis.