doc: improve & complete documentation on many sensors

Signed-off-by: Brendan Le Foll <brendan.le.foll@intel.com>

src/gas/README.txt

@@ -1,4 +1,4 @@
-Grove - Gas Sensor(MQ-2)：Combustible Gas、Smoke [middle sensitivity]
+Grove - Gas Sensor(MQ-2)：Combustible Gas Smoke [middle sensitivity]
 Grove - Gas Sensor(MQ-3)：Alcohol and Benzine [HIGH sensitivity] Long warmup
 Grove - Gas Sensor(MQ-5)：LPG, Natural Gas, Town Gas [high sensitivity]
 Grove - Gas Sensor(MQ-9)：LPG, CO, CH4 [low sensitivity]

src/gas/gas.h

@@ -38,7 +38,7 @@ namespace upm {
 /**
  * @brief C++ API for Gas sensors
  *
- * This file defines the Gas Analog sensors
+ * This file defines the Gas Analog sensors virtual functions
  */
 class Gas {
     public:

src/gas/mq2.h

@@ -31,7 +31,13 @@ namespace upm {
     /**
      * @brief C++ API for MQ2 gas sensor
      *
+     * The Grove - Gas Sensor (MQ2) module is useful for gas leakage detecting
+     * (in home and industry). It can detect LPG, i-butane, methane, alcohol,
+     * Hydrogen, smoke and other combustible gases. It's a medium sensitivity
+     * sensor with a detect concentration of 300-10000ppm.
+     *
      * @snippet mq2-example.cxx Interesting
+     * @image html grovegas.jpeg
      */
     class MQ2 : public Gas {
         public:

src/gas/mq3.h

@@ -31,7 +31,13 @@ namespace upm {
     /**
      * @brief C++ API for MQ3 gas sensor
      *
+     * The Grove MQ3 Gas Sensor module is useful for gas leakage detecting (in
+     * home and industry). It can detect Alcohol Vapour and Benzine. It's
+     * highly sensitive but has a long warmup time of about 1minute. It's
+     * detect rate is of 0.04-4mg/L Alcohol.
+     *
      * @snippet mq3-example.cxx Interesting
+     * @image html grovegas.jpeg
      */
     class MQ3 : public Gas {
         public:

src/gas/mq5.h

@@ -31,7 +31,13 @@ namespace upm {
     /**
      * @brief C++ API for MQ5 gas sensor
      *
+     * The Grove - Gas Sensor (MQ5) module is useful for gas leakage detecting
+     * (in home and industry). It can detect LPG, natural gas, town gas and so
+     * on. It is highly sensitive and has a detection concentration of
+     * 300-10000ppm.
+     *
      * @snippet mq5-example.cxx Interesting
+     * @image html grovegas.jpeg
      */
     class MQ5 : public Gas {
         public:

src/gas/mq9.h

@@ -31,7 +31,12 @@ namespace upm {
     /**
      * @brief C++ API for MQ9 gas sensor
      *
+     * The Grove MQ9 Gas Sensor module is useful for gas leakage detecting (in
+     * home and industry). It can detect Carbon Monoxide, Coal Gas and
+     * Liquefied Gas. It's sensitivty is 10-1000ppmCO 100-10000PPm Gas.
+     *
      * @snippet mq9-example.cxx Interesting
+     * @image html mq9.jpeg
      */
     class MQ9 : public Gas {
         public: