docs: more header files edited

Signed-off-by: Mihai Tudor Panu <mihai.tudor.panu@intel.com>

src/gas/mq9.h

@@ -36,11 +36,11 @@ namespace upm {
    * @man seeed
    * @con analog
    *
-   * @brief API for MQ9 Gas Sensor
+   * @brief API for the 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 sensitivity is 10-1000 ppm CO, 100-10000 ppm Gas.
+   * The Grove MQ9 Gas Sensor module is useful for gas leakage detection (in
+   * home and industry). It can detect carbon monoxide, coal gas, and
+   * liquefied gas. Its sensitivity is 10-1,000 ppm CO, and 100-10,000 ppm Gas.
    *
    * @image html mq3-9.jpeg
    * @snippet mq9.cxx Interesting
@@ -48,9 +48,9 @@ namespace upm {
     class MQ9 : public Gas {
         public:
             /**
-             * Jhd1313m1 constructor
+             * MQ9 constructor
              *
-             * @param gasPin analog pin where sensor is connected
+             * @param gasPin Analog pin where the sensor is connected
              */
             MQ9 (int gasPin);
 
@@ -60,7 +60,7 @@ namespace upm {
             ~MQ9 ();
 
             /**
-             * Return name of the component
+             * Returns the name of the sensor
              */
             std::string name()
             {