Add diagnostics module in OpenThread (#343)

* Add diagnostics module in OpenThread

  - provide the same diagnostics interface for both CLI and NCP usage
  - implement common diagnostics features based on existing platform interface defined in 'include/platform/'
  - other more platform specific diagnostics features will be processed under platform layer
  - update CLI interface to support diagnostics feature
  - update both Posix and CC2538 platform to support diagnostics feature

* Add diagnostics module unit test

   - move platform.h from "examples/platform" to "include/platform"
   - add test_diag.cpp to test diagnostics module

* Add a configuration option that would enable/disable diagnostics module

Add --enable-diag configuration option to enable/disable diagnostics module when building OpenThread.

include/platform/platform.h

@@ -0,0 +1,59 @@
+/*
+ *  Copyright (c) 2016, Nest Labs, Inc.
+ *  All rights reserved.
+ *
+ *  Redistribution and use in source and binary forms, with or without
+ *  modification, are permitted provided that the following conditions are met:
+ *  1. Redistributions of source code must retain the above copyright
+ *     notice, this list of conditions and the following disclaimer.
+ *  2. Redistributions in binary form must reproduce the above copyright
+ *     notice, this list of conditions and the following disclaimer in the
+ *     documentation and/or other materials provided with the distribution.
+ *  3. Neither the name of the copyright holder nor the
+ *     names of its contributors may be used to endorse or promote products
+ *     derived from this software without specific prior written permission.
+ *
+ *  THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
+ *  AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
+ *  IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
+ *  ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER OR CONTRIBUTORS BE
+ *  LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
+ *  CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
+ *  SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
+ *  INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
+ *  CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
+ *  ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
+ *  POSSIBILITY OF SUCH DAMAGE.
+ */
+
+/**
+ * @file
+ * @brief
+ *   This file defines the platform-specific initializers.
+ */
+
+#ifndef PLATFORM_H_
+#define PLATFORM_H_
+
+#ifdef __cplusplus
+extern "C" {
+#endif
+
+
+/**
+ * This function performs all platform-specific initialization.
+ *
+ */
+void PlatformInit(int argc, char *argv[]);
+
+/**
+ * This function performs all platform-specific processing.
+ *
+ */
+void PlatformProcessDrivers(void);
+
+#ifdef __cplusplus
+}  // end of extern "C"
+#endif
+
+#endif  // PLATFORM_H_