Pick up new implicit and explicit rules from the style guide

[krlmlr]

• Newline after multiline arguments? tidyverse/style#209
• Recommend single indent, not double indent tidyverse/style#223
• Mention empty curlies tidyverse/style#228: while() {}
• Add a section on vertical space tidyverse/style#227, i.e. not empty lines at beginning and end of function dec.
• Don't force the first switch argument in-line with switch( #858, i.e. add no line breaks to switch() if all fits on one line.
  More to come.

[IndrajeetPatil]

There are three parts to the "vertical space" item:

• Avoid empty lines at the start or end of functions. (Remove blank lines after opening and before closing braces #1195)
• Only use a single empty line when needed to separate functions or pipes. (Remove excessive line breaks between top-level expressions #1239)
• It often makes sense to put an empty line before a comment block, to help visually connect the explanation with the code that it applies to.

The third item is really not clear to me. What counts as a comment block? Anything that spans more than a single line?