Fix whitespace
Remove method duplicated in parent class
Add explicit mutator for dstr
Add explicit mutator for op_asgn
Add explicit mutator for or_asgn
Add explicit mutator for and_asgn
Change emit_nil to not emit on the left node of an assignment

* Add emit_nil to other nodes so that they can be replaced
  with nil, effectively removing them from the code.
Update flay threshold
Prefer constant over literal array
Collapse op_assign emitters into one
Merge pull request #110 from mbj/dstr-mutator

Dstr mutator