Fix version number in Doxyfile (0.3.5)

We need a way to automatically generate this from git tags in the
future...
diff --git a/Doxyfile b/Doxyfile
index 22d3bd6..6609d73 100644
--- a/Doxyfile
+++ b/Doxyfile
@@ -31,7 +31,7 @@
 # This could be handy for archiving the generated documentation or
 # if some version control system is used.
 
-PROJECT_NUMBER         = V1.0
+PROJECT_NUMBER         = V0.3.5
 
 # Using the PROJECT_BRIEF tag one can provide an optional one line description
 # for a project that appears at the top of each page and should give viewer