++RAC to hot-signal-lifetime for development
Stop prematurely disposing of output signals

Because we would dispose of build output subscriptions when the _signal
of signals_ was disposed (not the inner, flattened stream), it would
happen too early, resulting in no build output at all.

Instead, now that RAC is fixed, we can rely upon the lifetime of the
captured sinks we’re writing to. When the sink leaves scope, output
signals (and therefore observations) will automatically disappear too.

Fixes #151.
++RAC to improve-synchronous-cold-signals
Refactor users of ColdSignal for new API
Merge branch 'master' into fix-empty-build-logs
Merge branch 'master' into fix-empty-build-logs
Merge branch 'cold-signal-refactoring' into fix-empty-build-logs

Conflicts:
	Carthage.checkout/ReactiveCocoa
	CarthageKit/Task.swift
Bump Cartfile
Merge pull request #155 from Carthage/fix-empty-build-logs

Fix empty build logs