Grouped methods in Rotation doxygen.
Changes based on feedback from Sherm. Toggled "SHOW_INCLUDE_FILES" in Doxyfile to hide #includes. Collected and reorganized.
Merge pull request #262 from simbody/doxygen-groupRotationMethods

Grouped methods in Rotation doxygen.
Merge branch 'master' of github.com:simbody/simbody