Dev

[MrDomani]

Generally minor changes, preceding release to CRAN:

• Expanded description of the package.
• Added installation instructions.
• Added argument check to irank.
• Simplified iranks' handling of NA values - now with na.rm=FALSE an error is raised.
• Updated CITATION.
• Added cran-comments.md, as Hadley in his R Packages suggests.
• Spellcheck. inst/WORDLIST is a file with non-English words ignored while spellchecking.