For Travis CI - Demoting Doxygen's h1 to h2 and h2 to h3.
This process is only carried out when building Doxygen documentation pages in the CI server because those pages are intended to be embedded inside a Jekyll template.
Closes https://github.com/urho3d/urho3d.github.io/issues/3.
Also reverting back the scripting done for one time documentation build.
[ci skip]