i2c/i2c-tools: add i2c-tools example

1. add command i2cconfig
2. add command i2cdetect
3. add command i2cget
4. add command i2cset
5. add command i2cdump
6. add README.md

examples/peripherals/i2c/i2c_tools/main/cmd_i2ctools.h

@@ -0,0 +1,20 @@
+/* cmd_i2ctools.h
+
+   This example code is in the Public Domain (or CC0 licensed, at your option.)
+
+   Unless required by applicable law or agreed to in writing, this
+   software is distributed on an "AS IS" BASIS, WITHOUT WARRANTIES OR
+   CONDITIONS OF ANY KIND, either express or implied.
+*/
+
+#pragma once
+
+#ifdef __cplusplus
+extern "C" {
+#endif
+
+void register_i2ctools(void);
+
+#ifdef __cplusplus
+}
+#endif