update master from devel to 0.1.0.9001

[lorenzwalthert]

This pull request aims to merge latest developments in the package with master to the version 0.1.0.9001. The major differences to the current master 0.1.0.9001 are:

• updated documentation: Add missing arguments, spelling, formatting. Adding details how package methods deviate from base methods.
• improved performance of R CMD check: eliminated warnings. Previous: NO ERRORs, 2 WARNINGs, 1 NOTE.
• style: All lines of code are now (roughly) 80 characters long, T and F turned into explicit notation TRUE AND FALSE.
• cut.integer: floor is used rather than round when breaks are supplied as decimal numbers. The quantile method was dropped.
• index_cfactor: arguments only recycled if length 1 (Previously if full recycling was possible).

[codecov-io]

Current coverage is 77.65% (diff: 67.80%)

Merging #14 into master will decrease coverage by 11.51%

@@             master        #14   diff @@
==========================================
  Files             4          4          
  Lines           157        273   +116   
  Methods           0          0          
  Messages          0          0          
  Branches          0          0          
==========================================
+ Hits            140        212    +72   
- Misses           17         61    +44   
  Partials          0          0          

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