Add N_TRUE and N_FALSE node helpers
Fix code formatting
Add binary connective mutator
Remove :not node

* The :not node is not used in Ruby 1.9+
Update flay threshold
Move true and false nodes above nil
Change connective mutator to mutate the operand boolean context
Fix whitespace
Add Mutant::NodeHelpers#n_not
Refactor Mutator::Node::Connective::Binary#mutate_operands
Refactor Mutant::Mutator::Node::If#mutate_condition
Merge pull request #76 from mbj/connective-mutator

Connective mutator