update to carthage 0.4 directory structure
write tests for to-be-implemented merge function for a sequence of HotSignals
write merge function for ColdSignal of HotSignals
give HotSignal a merge class function that takes a SequenceType
add mergeWith convenience function and change a line in the spec to test it
forgot a <T>
revert last 2 commits to remove mergeWith convenience function
remove merge for ColdSignal of HotSignals; instead use HotSignal.pipe() and .merge() in the new merge(SequenceType)
Merge pull request #1648 from jconst/swift-development

More ways to merge HotSignals; Update to carthage 0.4