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/javaupm_o2.i

@@ -0,0 +1,19 @@
+%module javaupm_o2
+%include "../upm.i"
+
+%{
+    #include "o2.hpp"
+%}
+
+%include "o2.hpp"
+
+%pragma(java) jniclasscode=%{
+    static {
+        try {
+            System.loadLibrary("javaupm_o2");
+        } catch (UnsatisfiedLinkError e) {
+            System.err.println("Native code library failed to load. \n" + e);
+            System.exit(1);
+        }
+    }
+%}