created ZSTD_compress2() and ZSTD_compressStream2()

ZSTD_compress_generic() is renamed ZSTD_compressStream2().

Note that, for the time being,
the "stable" API and advanced one use different parameter planes :
setting parameters using the advanced API does not influence ZSTD_compressStream()
and using ZSTD_initCStream() does not influence parameters for ZSTD_compressStream2().

tests/fuzz/simple_round_trip.c

@@ -42,7 +42,7 @@ static size_t roundTripTest(void *result, size_t resultCapacity,
 
         ZSTD_CCtx_reset(cctx, ZSTD_reset_session_only);
         FUZZ_setRandomParameters(cctx, srcSize, &seed);
-        err = ZSTD_compress_generic(cctx, &out, &in, ZSTD_e_end);
+        err = ZSTD_compressStream2(cctx, &out, &in, ZSTD_e_end);
         FUZZ_ZASSERT(err);
         FUZZ_ASSERT(err == 0);
         cSize = out.pos;