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/.gitignore b/.gitignore
index 799619f..07e92ea 100644
--- a/.gitignore
+++ b/.gitignore
@@ -25,3 +25,4 @@
 .idea/
 cmake-build-debug/
 Testing
+html