Full sketch + example of SafeSource (KeepSafe +Ack) pattern.

TODO: tuple->serialise() should be a no-op for all cases. Currently if
KeepSafe stores the iput hash instead of the copied hash there is a
difference (most likely capacity related?). This would be a nice to fix.

fixes #25 - Will add more to this later. Banshee is a demonstrative
release.