o2: Added O2 sensor C source

Added the C source for the O2 sensor with necessary changes to cmake,
examples, docs.

    * Renamed all files with groveo2 to o2
    * Replaced all instances of groveo2 with o2
    * Added C source for o2 sensor
    * Updated all cmake files
    * Added C example for o2 sensor

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

src/o2/pyupm_o2.i

@@ -0,0 +1,11 @@
+// Include doxygen-generated documentation
+%include "pyupm_doxy2swig.i"
+%module pyupm_o2
+%include "../upm.i"
+
+%feature("autodoc", "3");
+
+%include "o2.hpp"
+%{
+    #include "o2.hpp"
+%}