Implement preprocessors via the emitter pattern
Style
Whitlelist rubocop reported issue
Adjust flay score
Adjust flay threshold
Fix blind spots in preprocessor
Address reek reported smells
Kill mutations in Morpher::Node#initialize
Kill mutations in Morpher::Registry

Currently this lib is mutation covered via implicit coverage. Later I'll
move to explicit one!
Kill mutation in Morpher::Printer
Remove dead code
Kill Mutation in Morpher::Printer::Mixin