Add file: scheme to links

See http://qt.gitorious.org/qt/qt/commit/5f161591b6ae25524b129bf4a41d6438f0a4d402 and https://bugreports.qt-project.org/browse/QTBUG-24077
Due to security reasons, links without scheme are not loaded.
Merge pull request #138 from janosvitok/doc-fixes

Doc fixes