Fixed doxygen function-grouping.
\defgroup was used to describe the groups of functions, but that is supposed to
group classes and files into modules.  The grouping of functions was correct in
the code and the \defgroup tags just needed to be changed to \name tags, which then
group the functions nicely within the same page.
Merge pull request #102 from ros-planning/fix-defgroup-doxygen

Fixed doxygen function-grouping.