Add a TSL4531 driver and example

examples/tsl4531/Makefile

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+PROGRAM=tsl4531_example
+EXTRA_COMPONENTS = extras/i2c extras/tsl4531
+include ../../common.mk

examples/tsl4531/tsl4531_example.c

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+/*
+ * This sample code is in the public domain.
+ */
+
+#include <stdio.h>
+#include <stdlib.h>
+#include "esp/uart.h"
+#include "FreeRTOS.h"
+#include "i2c/i2c.h"
+#include "task.h"
+#include "tsl4531/tsl4531.h"
+
+/* An example using the TSL4531 light sensor
+ * to read and print lux values from a sensor
+ * attached to GPIO pin 2 (SCL) and GPIO pin 0 (SDA)
+ * Connect 3.3v from the ESP to Vin and GND to GND
+ */
+
+#define SCL_PIN (2)
+#define SDA_PIN (0)
+
+void tsl4531MeasurementTask(void *pvParameters)
+{
+    tsl4531_t lightSensor;
+    lightSensor.i2c_addr = TSL4531_I2C_ADDR;
+    tsl4531_init(&lightSensor);
+
+    tsl4531_set_integration_time(&lightSensor, TSL4531_INTEGRATION_400MS);
+    tsl4531_set_power_save_skip(&lightSensor, true);
+
+    uint16_t lux = 0;
+
+    while (1)
+    {
+        if (tsl4531_read_lux(&lightSensor, &lux))
+        {
+            printf("Lux: %u\n", lux);
+        }
+        else
+        {
+            printf("Could not read data from TSL4531\n");
+        }
+
+        // 0.05 second delay
+        vTaskDelay(50 / portTICK_PERIOD_MS);
+    }
+}
+
+void user_init(void)
+{
+    uart_set_baud(0, 115200);
+    i2c_init(SCL_PIN, SDA_PIN);
+
+    xTaskCreate(tsl4531MeasurementTask, "tsl4531MeasurementTask", 256, NULL, 2, NULL);
+}