Make sure Vanuatoo doesn't throw trivial StackOverflows..
Simplify flattened pre/post
Strings support, fix printing of method calls

- Introduce Leon strings (smt-based solvers only)
  Available in leon.lang.string._

- Print method calls properly, specialize binary ops
Complete support for strings in evaluator/simplestValue
Add script for testing solvers
Always include lib
Use imports
Treat <empty> package
Extract string literals in degenerate cases
Getting active functions, visible from main units + main units
List literals
Synthesis framework refactoring
Fix tests with new synthesis refactoring
Single non-main Units get printed
Imports show to fresh Modules during MethodLifting
Imports show to fresh Modules after RestoreMethods
Literal patterns
Option.get in Leon library
Make constructors of Expr subclasses with companion .apply methods private
make isGround a public method