Display Backlight: automatically adjust to ambient sensor reading

This registers a Task, reading the ambient light sensor and adjusting the display backlight accordingly

fixes #95

epicardium/modules/brightness.c

+#include "epicardium.h"
+#include "modules.h"
+#include "log.h"
+
+bool _autobrightness_enabled = true;
+
+void vAutoBrightnessTask(void *pvParameters)
+{
+	vTaskDelay(pdMS_TO_TICKS(500));
+
+	while (epic_light_sensor_run() < 0)
+		LOG_CRIT("autobrightness", "Could not start ambient sensor");
+
+	while (1) {
+		vTaskDelay(pdMS_TO_TICKS(1000));
+		if (_autobrightness_enabled) {
+			unsigned short int light;
+			if (epic_light_sensor_get(&light) < 0) {
+				LOG_CRIT("autobrightness", "Could not read light sensor");
+				continue;
+			}
+
+			unsigned short int brightness;
+
+			if (light > 199)
+				brightness = 100;
+			else
+				brightness = light / 2 + 1;
+
+			if (epic_disp_open() < 0)
+				continue;
+
+			epic_disp_backlight(brightness);
+			epic_disp_close();
+		}
+	}
+}