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/main/uart_echo_example_main.c

@@ -0,0 +1,73 @@
+/* Uart Events Example
+
+   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.
+*/
+#include <stdio.h>
+#include <string.h>
+#include <stdlib.h>
+#include "freertos/FreeRTOS.h"
+#include "freertos/task.h"
+#include "esp_system.h"
+#include "nvs_flash.h"
+#include "driver/uart.h"
+#include "freertos/queue.h"
+#include "esp_log.h"
+#include "soc/uart_struct.h"
+
+/**
+ * This is a example exaple which echos any data it receives on UART1 back to the sender, with hardware flow control
+ * turned on. It does not use UART driver event queue.
+ *
+ * - port: UART1
+ * - rx buffer: on
+ * - tx buffer: off
+ * - flow control: on
+ * - event queue: off
+ * - pin assignment: txd(io4), rxd(io5), rts(18), cts(19)
+ */
+
+#define ECHO_TEST_TXD  (4)
+#define ECHO_TEST_RXD  (5)
+#define ECHO_TEST_RTS  (18)
+#define ECHO_TEST_CTS  (19)
+
+#define BUF_SIZE (1024)
+
+//an example of echo test with hardware flow control on UART1
+static void echo_task()
+{
+    const int uart_num = UART_NUM_1;
+    uart_config_t uart_config = {
+        .baud_rate = 115200,
+        .data_bits = UART_DATA_8_BITS,
+        .parity = UART_PARITY_DISABLE,
+        .stop_bits = UART_STOP_BITS_1,
+        .flow_ctrl = UART_HW_FLOWCTRL_CTS_RTS,
+        .rx_flow_ctrl_thresh = 122,
+    };
+    //Configure UART1 parameters
+    uart_param_config(uart_num, &uart_config);
+    //Set UART1 pins(TX: IO4, RX: I05, RTS: IO18, CTS: IO19)
+    uart_set_pin(uart_num, ECHO_TEST_TXD, ECHO_TEST_RXD, ECHO_TEST_RTS, ECHO_TEST_CTS);
+    //Install UART driver (we don't need an event queue here)
+    //In this example we don't even use a buffer for sending data.
+    uart_driver_install(uart_num, BUF_SIZE * 2, 0, 0, NULL, 0);
+
+    uint8_t* data = (uint8_t*) malloc(BUF_SIZE);
+    while(1) {
+        //Read data from UART
+        int len = uart_read_bytes(uart_num, data, BUF_SIZE, 20 / portTICK_RATE_MS);
+        //Write data back to UART
+        uart_write_bytes(uart_num, (const char*) data, len);
+    }
+}
+
+void app_main()
+{
+    //A uart read/write example without event queue;
+    xTaskCreate(echo_task, "uart_echo_task", 1024, NULL, 10, NULL);
+}