Enable the semantic version mechanism for WAMR (#1374)

Use the semantic versioning (https://semver.org) to replace the current date
versioning system, which is more general and is requested by some developers,
e.g. issue #1357.

There are three parts in the new version string:
- major. Any incompatible modification on ABIs and APIs will lead to an increment
  in the value of major, which mainly includes: AOT calling conventions, AOT file
  format, wasm_export.h, wasm_c_api.h, and so on.
- minor. It represents new features, including MVP/POST-MVP features, libraries,
  WAMR private ones, and so one.
- patch. It represents patches.

The new version will start from 1.0.0. Update the help info and version showing for
iwasm and wamrc.

core/version.h.in

@@ -0,0 +1,14 @@
+/*
+ * Copyright (C) 2019 Intel Corporation.  All rights reserved.
+ * SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+ */
+
+/* Please don't modify this header. It is automatically generated.
+   Any modification should be in config_common.cmake */
+
+#ifndef _WAMR_VERSION_H_
+#define _WAMR_VERSION_H_
+#cmakedefine WAMR_VERSION_MAJOR @WAMR_VERSION_MAJOR@
+#define WAMR_VERSION_MINOR @WAMR_VERSION_MINOR@
+#define WAMR_VERSION_PATCH @WAMR_VERSION_PATCH@
+#endif