first pass on novice r reference sheet
re-ordered sections to follow python, still have R specific
removed bad-mouthing loops
deleted extra line
fixed code tags, contition, data frame spelling, update packages
parameters to arguments
spelling mistake, moved string split with str concatenation
followed python ref sheet for overall order and content
added examples for if, for, functions
example for apply (same as mentioned in lesson 01)
replaced html code block syntax with md backtick
removed sections:  R, working with data, plotting, processing mult files
fixed indentation, spacing, and line breaks for multi line code blocks
Merge pull request #672 from chendaniely/R-cheatsheet

first pass on novice r reference sheet