Refactored BeLogical. Added beTrue() and beFalse() matchers. Closes #24
Added beTrue() and beFalse() for objc.

Republicized toImpl and toNotImpl by not inheritanting protocols.
Merge pull request #43 from jeffh/beTrue-beFalse-matchers

Refactored BeLogical. Added beTrue() and beFalse() matchers. Closes #24