cwlsxxa: Initial implementation

The driver was developed using the Veris CWLSHTA CO2 Gas sensor.  The
'T' variant supports a temperature sensor, and the 'H' variant
supports a humidity sensor.

All 3 signals are provided by the device as analog 0-5Vdc, 0-10Vdc, or
4-20ma loop current outputs.  For devices supporting temperature, the
valid temperature range is 10C to 50C.  The humidity ranges from 0% to
100% (non-condensing).  The CO2 sensor ranges from 0 to 2000 ppm.

This driver was developed using the 5Vdc outputs and the 4-20ma
outputs.  For voltage outputs, your MCU must be configured for 5V
operation.  In addition, you must configure the sensor (via it's
configuration switches) to output 0-5VDC only.  Using any other analog
reference voltage will require the appropriate external circuitry
(such as a voltage divider) in order to interface safely with your
MCU.

In addition, the sensor can be configured for 4-20ma usage, by
specifying the correct receiver resistance (in ohms) in the
constructor.  This sensor was tested with a Cooking Hacks (Libelium)
4-channel 4-20ma Arduino interface shield.  For this interface, the
receiver resistance was specified as 165.0 ohms.

Signed-off-by: Jon Trulson <jtrulson@ics.com>
Signed-off-by: Abhishek Malik <abhishek.malik@intel.com>

examples/c++/CMakeLists.txt

@@ -248,6 +248,7 @@ add_example (max44009)
 add_example (si1132)
 add_example (si7005)
 add_example (t6713)
+add_example (cwlsxxa)
 
 # These are special cases where you specify example binary, source file and module(s)
 include_directories (${PROJECT_SOURCE_DIR}/src)