Hard coded path to doxygen/xml/index.xml

[Sebanisu]

I found it in the conf.py

breathe_projects = { 'j' : '/home/cph/jsource/build/docs/doxygen/xml'}

I'm thinking this is set correctly in CMakeLists.txt. So should be a way to import the variable into conf.py.

set(DOXYGEN_OUTPUT_DIR ${CMAKE_CURRENT_BINARY_DIR}/doxygen)
set(DOXYGEN_INDEX_FILE ${DOXYGEN_OUTPUT_DIR}/xml/index.xml)

[Sebanisu]

Locally I changed this to a relative path in conf.py. and that seemed to work.
Will do a pull request.