Added documentation for analysis tools

src/analysis/AnalysisBase.cpp

src/analysis/AnalysisWithDataCollection.cpp

src/analysis/EuclideanDissimilarityMatrix.cpp

src/analysis/FarthestPointSampling.cpp

src/analysis/LandmarkSelectionBase.cpp

src/analysis/LandmarkSelectionBase.h

src/analysis/OutputColvarFile.cpp

src/analysis/OutputPDBFile.cpp

src/analysis/PrintDissimilarityMatrix.cpp

src/analysis/ReadDissimilarityMatrix.cpp

src/analysis/SelectWithStride.cpp

src/dimred/ClassicalMultiDimensionalScaling.cpp

src/dimred/ProjectNonLandmarkPoints.cpp

src/dimred/SketchMapPointwise.cpp

src/dimred/SketchMapSmacof.cpp

src/dimred/SmacoffMDS.cpp

src/multicolvar/DumpMultiColvar.cpp

src/multicolvar/MultiColvarDensity.cpp

src/tools/Keywords.cpp

src/tools/Keywords.h