Fix typos
Extract 4 Parser warning cops from Syntax cop
Convert Syntax cop to a module

It no longer interacts with Commissioner, and it reports only
fatal/error offences that cannot be disabled.
Improve AmbiguousRegexpLiteral offence message
Improve AmbiguousOperator offence message
Improve InvalidCharacterLiteral offence message
Merge pull request #719 from yujinakayama/split-syntax-cop

Split Syntax cop