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/mhz16/CMakeLists.txt

@@ -1,5 +1,5 @@
 set (libname "mhz16")
-set (libdescription "Grove CO2 sensor")
+set (libdescription "CO2 Sensor")
 set (module_src ${libname}.cxx)
 set (module_hpp ${libname}.hpp)
 upm_module_init(mraa)

src/mhz16/mhz16.hpp

@@ -56,11 +56,12 @@ namespace upm {
     /**
      * @library mhz16
      * @sensor mhz16
-     * @comname Grove CO2 Sensor
+     * @comname CO2 Sensor
      * @altname MHZ16 Serial CO2 Sensor
      * @type gaseous
      * @man seeed
      * @con uart
+     * @web http://wiki.seeed.cc/Grove-CO2_Sensor/
      *
      * @brief API support for the Grove CO2 sensor
      *