improve docs

Fltk/pluginWindow.cpp

Plugin/Annotate.cpp

Plugin/Curl.cpp

Plugin/CutGrid.cpp

Plugin/CutParametric.cpp

Plugin/CutPlane.cpp

Plugin/CutSphere.cpp

Plugin/Divergence.cpp

Plugin/Eigenvalues.cpp

Plugin/Eigenvectors.cpp

Plugin/ExtractElements.cpp

Plugin/GSHHS.cpp

Plugin/Gradient.cpp

Plugin/HarmonicToTime.cpp

Plugin/HomologyComputation.cpp

Plugin/Integrate.cpp

Plugin/Isosurface.cpp

Plugin/Lambda2.cpp

Plugin/LongitudeLatitude.cpp

Plugin/MakeSimplex.cpp