Check and update documentation files to make them more informative

[Xinqiu Yao]

An example is the documentation for rmsf(), which is too short at current stage as indicated by one of our user:

"More detail on how RMSF calculations are perfromed and how those results could be interpreted might be useful for others. It seems this page is particularly lacking in detailed when compared to the rest of the documenation which I might add is excellent."