Improve case/when indentation example
[Fix #179] Add examples of multi-line conditional assignment
Extend an example
Fix a couple of typos
Reword usage of empty lines explanation

The original wording surrounding using empty lines to create visual
separations for readability was itself hard to read.

This commit rewords the explanation to clarify the original point.
Add a rule about redundant RuntimeError
Add a rule about fail/raise arguments
No space after !
Merge pull request #229 from trlinkin/fix_and

Remove misplaced "and"
[Fix #175] Add a rule about !!
Add a rule about the indentation of multi-line array literals
Clarify !! rule
Reword !! rule