doc: Scrubbed ALL sensor library descriptions

In an effort to clean-up and standardize UPM library
documentation, this commit updates (and in most cases,
unifies) the CMake description string AND CXX header
@comname string.

Strings were taken from datasheets when possible, spelling
mistakes were addressed, copy/paste errors where fixed,
Title Case was used, etc.

    * Tested/updated/added @web tags
    * Added/updated invalid sensor images
    * Added/updated @man tags, added missing manufacturers

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

src/gas/mq8.hpp

@@ -31,10 +31,11 @@ namespace upm {
   /**
    * @library gas
    * @sensor mq8
-   * @comname DFRobot MQ8 CO Gas Sensor
+   * @comname MQ8 Flammable (Hydrogen) Gas Sensor
    * @type gaseous
    * @man dfrobot
    * @con analog
+   * @web https://www.dfrobot.com/wiki/index.php/Hydrogen_Gas_Sensor(MQ8)_(SKU:SEN0133)
    *
    * @brief API for the DFRobot MQ8 Hydrogen (H2) Gas Sensor
    *