docs: Add minimal doxygen setup

Add a Doxyfile and the minimum required tags to the sources to make
anything useful appear in the documentation.

To generate just run: doxygen from the project root or doxygen
./Doxyfile.

Change-Id: Ie60eb1458586dc0a7843dca69e969b78817260d3
Signed-off-by: Brad Bishop <bradleyb@fuzziesquirrel.com>
diff --git a/src/Overlay.cpp b/src/Overlay.cpp
index edd00f7..cb6ed10 100644
--- a/src/Overlay.cpp
+++ b/src/Overlay.cpp
@@ -13,6 +13,7 @@
 // See the License for the specific language governing permissions and
 // limitations under the License.
 */
+/// \file Overlay.cpp
 
 #include "Overlay.hpp"