Working on Z3 solvers

src/main/scala/inox/ast/Extractors.scala

src/main/scala/inox/solvers/Solver.scala

src/main/scala/inox/solvers/SolverResponses.scala

src/main/scala/inox/solvers/unrolling/UnrollingSolver.scala

src/main/scala/inox/solvers/z3/AbstractZ3Solver.scala

src/main/scala/inox/solvers/z3/FairZ3Solver.scala

src/main/scala/inox/solvers/z3/Z3Solver.scala

src/main/scala/inox/solvers/z3/Z3UnrollingSolver.scala