Quick is the 1st BDD framework to support Xcode 6

This fixes issue #1: Xcode test navigator integration.

As of Xcode 6, each test invocation's selector is used to determine the
name displayed in the test navigator. Specta and Quick both used the
same instance method (`-[QuickSpec runExampleAtIndex:]`, in Quick's
case) to run each example. As a result, all tests in the same spec had
the same name, causing each example to "overwrite" each previous one in
the navigator. This caused several issues, including red lines to
indicate test failure in Xcode suddenly disappearing when the next
example finished running.

During `+[QuickSpec testInvocations]`, define a new instance method for
each example. Then, return an invocation that executes that new instance
method