Documentation of package components

[diyadas]

As per openjournals/joss-reviews#1321

Largely excellent, just a few missing pieces.

• moco: description is incomplete
• unclear from documentation how to use coph.tocher, cophenetic.tocher, D2.disc.default, plot.genecovtest, plot.singh, predict.D2.disc, print.gencovtest, print.tocher, singh.default, tocher.dist (listed in package contents, but unclear if meant to be called directly)
• Most of the example code for sHe is commented out?

[arsilva87]

@diyadas

• description updated
• all those functions are S3 methods or alias for the functions that are directly called (print, plot...)
• Most of the code was set not to run on tests, as they are time demanding.