Hi Daniel, it looks like the doxygen link on
<http://clang.llvm.org/extra/> is dead. Could you look into it? The
`doxygen` makefile target needs to be run, and it places the doxygen
output alongside the sphinx output in a doxygen directory (i.e.
index.rst -> `_build/html/index.html` and doxygen puts its main page
-- Sean Silva