add TVOC option

Author: ladyada

Adafruit_Sensor.h

@@ -66,7 +66,8 @@ typedef enum {
   SENSOR_TYPE_OBJECT_TEMPERATURE = (14),
   SENSOR_TYPE_VOLTAGE = (15),
   SENSOR_TYPE_CURRENT = (16),
-  SENSOR_TYPE_COLOR = (17)
+  SENSOR_TYPE_COLOR = (17),
+  SENSOR_TYPE_TVOC = (18)
 } sensors_type_t;
 
 /** struct sensors_vec_s is used to return a vector in a common format. */
@@ -134,6 +135,7 @@ typedef struct {
     float relative_humidity; /**< relative humidity in percent */
     float current;           /**< current in milliamps (mA) */
     float voltage;           /**< voltage in volts (V) */
+    float tvoc;              /**< Total Volatile Organic Compounds, in ppb */
     sensors_color_t color;   /**< color in RGB component values */
   };                         ///< Union for the wide ranges of data we can carry
 } sensors_event_t;