Fix code formatting
Refactor scope and method regexps
Change Mutant::CLI::Classifier#matcher to be private
Change Mutant::CLI::Classifier::Method#matcher to be private
Remove Mutant::CLI::Classifier::Method#identification

* This is a duplicate of #identifer in the parent class
Update method not found to raise a NameError
Update constant lookup to use stricter approach
Update metrics thresholds