New cop Style/EmptyElse

Checks for empty `else`-clauses, i.e. clauses containing nothing but comments
and/or an explicit ending `nil`.
Correct some spelling errors
Merge pull request #1476 from jonas054/fix_spelling

Correct some spelling errors
Merge pull request #1444 from Koronen/vk-else-nil

New cop Style/ElseNil
Add ExtraSpacing cop that detects unnecessary whitespace.