small fixes to let the package pass `R CMD check`#5

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rnuske wants to merge 5 commits intoAWF-GAUG:masterfrom rnuske:master

+87-69

Commits on Feb 14, 2020

remove superfluous help pages
Robert Nuske
committed
make global variables known to check
Robert Nuske
committed
add required package stats to DESCRIPTION and clean up Depends and Imports
Robert Nuske
committed
fix inconsistencies between variable names in function and documentation
Robert Nuske
committed
add basic documentation for dataset ramdom_tree
Robert Nuske
committed