v0.4.0

• Fix: Possible crash caused by missing response object (#26)
• Fix: Anticipating rounding errors in progress checks (#16)
• Fix: Potential crashes caused by improper resource management (#25, #19)
• Feature: Add safe methods to perform state changes and adjustments,
  i.e., tryFulfil:, tryFail: and tryProgress:.
• Feature: Add methods waitForResultWithin: and waitForErrorWithin: to
  simplify testing asynchronous code.
• Feature: Add new collect: combinator: it collects all outcomes of the
  supplied promises, i.e., errors and values. Thus it never fails.
• Feature: Add new relay: combinator: Relays all promise events to a
  specified deferred.
• Feature: Add new always: and always:on: callback handlers.