\usepackage{fixltx2e} must come before use \usepackage{float}

The \usepackage{doxygen} statement adds float as a depenency.
If the order is wrong the latex generation fails with:
LaTeX Error: Unknown float option `H'
Merge pull request #178 from ellert/master

\usepackage{fixltx2e} must come before use \usepackage{float}