Remove BasicMatcher and NonNilBasicMatcher

[modocache]

See the discussion for details: #95 (comment)

Basically, implementing "meta-matchers" (matchers that are composed from other matchers, like allPass() and Guanaco's haveSucceeded() and haveFailed() is made difficult by the fact that matchers could be one of three distinct, unrelated types: Matcher, BasicMatcher, and NonNilBasicMatcher.

It should be easy to define a function that takes a matcher without defining three signatures, like allPass() does:

public func allPass<U,V where U: SequenceType, V: NonNilBasicMatcher, U.Generator.Element == V.ValueType>(matcher: V) -> NonNilMatcherFunc<U>
public func allPass<U,V where U: SequenceType, V: BasicMatcher, U.Generator.Element == V.ValueType>(matcher: V) -> NonNilMatcherFunc<U>
public func allPass<U,V where U: SequenceType, V: Matcher, U.Generator.Element == V.ValueType>(matcher: V) -> NonNilMatcherFunc<U>

In the linked discussion, @jeffh elaborates:

Yeah, there needs to be some changes to simplify the internals. I think the removal of BasicMatcher and NonNilBasicMatcher would be preferred in some way. There also needs a reinvestigation if the Swift compiler still gives an obscure message when a generic does match optionals. Having the matcher be able to specify that while Nimble's expectation and matcher protocols be ignorant of that detail would be best.