Remove complexity in shared mutator examples
Use unparser from git source
Show backtrace for failures under guard
Add child nameing helpers
Use constant nodes when possible
Use child nameing in argument mutator
Fix edge cases in begin mutator
Fix edge cases in block mutator
Use child nameing in define mutator
Use child nameing in if mutator
Use child nameing in while mutator and fix edge cases
Add spec for block pass send mutations