issue 118 ambient light sensor max framerate

since freertos ticks at 1kHz i can't really use it for super fast input, so i just put in a direct access. precise timing kinda is the user's problem. each read has an overhead of ~240us, you might wanna add a 100-300us delay with utime.sleep_us for stability though.

epicardium/modules/light_sensor.c

@@ -27,6 +27,13 @@ static int light_sensor_init()
 	return 0;
 }
 
+uint16_t epic_light_sensor_read()
+{
+	ADC_StartConvert(ADC_CH_7, 0, 0);
+	ADC_GetData(&last_value);
+	return last_value;
+}
+
 static void readAdcCallback()
 {
 	if (hwlock_acquire(HWLOCK_ADC, 0) != 0) {