add boolean support for cmp matcher

[chris-rock]

cmp matcher learns the comparison of string values with boolean values:

describe true do
    it { should cmp 'true' }
    it { should cmp 'True' }
    it { should cmp true }
  end

  describe false do
    it { should cmp 'false' }
    it { should cmp 'False' }
    it { should cmp false }
  end

[arlimus]

This should get us to feature-completion on cmp, awesome addition @chris-rock 👍
kudos !!