esp_netif_init() returns standard esp_err_t error code (unlike tcpip_adapter init), so shall be checked for the return value
Also to make the initialization code more consistent.
* Use "example" in all example function & variable names,
ie use i2c_example_xxx instead of i2c_xxx for example functions.
Closes#198https://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
nvs_flash_init may return an error code in some cases, and applications
should check this error code (or at least assert on it being ESP_OK, to
make potential issues more immediately obvious).
This change modifies all the examples which use NVS to check the error
code. Most examples get a simple ESP_ERROR_CHECK assert, while NVS
examples, OTA example, and NVS unit tests get a more verbose check which
may be used in real applications.
