[Fix #223] Cover use of {} in argument hash

Explicitly cover whether {} should be used around options hashes being
passed to methods
Merge pull request #226 from meagar/master

[Fix #223] Cover use of {} in argument hash
[Fix #221] Reword rule about Hash#fetch and default values
Fix missing Ruby statement for code highlight
Merge pull request #228 from shamanime/patch-1

Fix missing Ruby statement for code highlight
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.
Made naming directions of predicate methods a bit more specific
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
Fix example of heredoc result