examples: Standardise naming of files, symbols, etc. in examples

* Use "example" in all example function & variable names,
  ie use i2c_example_xxx instead of i2c_xxx for example functions.
  Closes #198 https://github.com/espressif/esp-idf/issues/198
* Mark example functions, etc. static
* Replace uses of "test" & "demo" with "example"
* Split the UART example into two
* Rename "main" example files to end with "_main.c" for disambiguation

examples/peripherals/uart_echo/Makefile

@@ -0,0 +1,9 @@
+#
+# This is a project Makefile. It is assumed the directory this Makefile resides in is a
+# project subdirectory.
+#
+
+PROJECT_NAME := uart_echo
+
+include $(IDF_PATH)/make/project.mk
+