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/htu21d/CMakeLists.txt

@@ -1,5 +1,5 @@
 set (libname "htu21d")
-set (libdescription "Humidity Sensor")
+set (libdescription "Digital Relative Humidity Sensor with Temperature")
 set (module_src ${libname}.cpp)
 set (module_hpp ${libname}.hpp)
 upm_module_init(mraa)

src/htu21d/htu21d.hpp

@@ -57,7 +57,7 @@ namespace upm {
 /**
  * @library htu21d
  * @sensor htu21d
- * @comname HTU21D Temperature & Humidity Sensor
+ * @comname Digital Relative Humidity Sensor with Temperature
  * @type temp
  * @man seeed adafruit sparkfun
  * @web http://www.meas-spec.com/downloads/HTU21D.pdf