[release] Update header and displayed version for release 0.2

src/printers/marabou.ml

src/printers/pyrat.ml

src/printers/vnnlib.ml

src/proof_strategy.ml

src/proof_strategy.mli

src/prover.ml

src/prover.mli

src/reduction_engine.ml

src/reduction_engine.mli

src/saver.ml

src/saver.mli

src/transformations/native_nn_prover.ml

src/transformations/native_nn_prover.mli

src/transformations/nn2smt.ml

src/transformations/nn2smt.mli

src/transformations/simplify_rel.ml

src/transformations/simplify_rel.mli

src/transformations/split.ml

src/transformations/split.mli

src/transformations/utils.ml