snippet: Updated all snippet tags

Ensure all src C++ headers which have corresponding C++ examples have
doxygen tags which point to those examples.  Some were missing, some
were invalid, some needed to be updated to match the new example names.

Signed-off-by: Noel Eck <noel.eck@intel.com>

src/gas/mq2.hpp

@@ -46,7 +46,7 @@ namespace upm {
    * sensor with a detection range of 300-10,000 ppm.
    *
    * @image html mq2-5.jpeg
-   * @snippet mq2.cxx Interesting
+   * @snippet gas-mq2.cxx Interesting
    */
     class MQ2 : public Gas {
         public:

src/gas/mq3.hpp

@@ -45,7 +45,7 @@ namespace upm {
    * detection range is 0.04-4 mg/L Alcohol.
    *
    * @image html mq3-9.jpeg
-   * @snippet mq3.cxx Interesting
+   * @snippet gas-mq3.cxx Interesting
    */
     class MQ3 : public Gas {
         public:

src/gas/mq4.hpp

@@ -47,7 +47,7 @@ namespace upm {
    * at least 24 hours.  See the datasheet for details.
    *
    * @image html mq2-5.jpeg
-   * @snippet mq4.cxx Interesting
+   * @snippet gas-mq4.cxx Interesting
    */
     class MQ4 : public Gas {
         public:

src/gas/mq5.hpp

@@ -46,7 +46,7 @@ namespace upm {
    * 300-10,000 ppm.
    *
    * @image html mq2-5.jpeg
-   * @snippet mq5.cxx Interesting
+   * @snippet gas-mq5.cxx Interesting
    */
     class MQ5 : public Gas {
         public:

src/gas/mq6.hpp

@@ -47,7 +47,7 @@ namespace upm {
    * at least 24 hours.  See the datasheet for details.
    *
    * @image html mq2-5.jpeg
-   * @snippet mq6.cxx Interesting
+   * @snippet gas-mq6.cxx Interesting
    */
     class MQ6 : public Gas {
         public:

src/gas/mq7.hpp

@@ -47,7 +47,7 @@ namespace upm {
    * 48 hours.  See the datasheet for details.
    *
    * @image html mq3-9.jpeg
-   * @snippet mq7.cxx Interesting
+   * @snippet gas-mq7.cxx Interesting
    */
     class MQ7 : public Gas {
         public:

src/gas/mq8.hpp

@@ -47,7 +47,7 @@ namespace upm {
    * at least 24 hours.  See the datasheet for details.
    *
    * @image html mq2-5.jpeg
-   * @snippet mq8.cxx Interesting
+   * @snippet gas-mq8.cxx Interesting
    */
     class MQ8 : public Gas {
         public:

src/gas/mq9.hpp

@@ -44,7 +44,7 @@ namespace upm {
    * 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
+   * @snippet gas-mq9.cxx Interesting
    */
     class MQ9 : public Gas {
         public:

src/gas/tp401.hpp

@@ -50,7 +50,7 @@ namespace upm {
    * operation to stabilize completely.
    *
    * @image html tp401.jpeg
-   * @snippet tp401.cxx Interesting
+   * @snippet gas-tp401.cxx Interesting
    */
     class TP401 : public Gas {
         public: