This commit adds a new struct, `stateStep`, to decide the workflow
inside `resumePayment`.
It also refactors `collectResultAsync` introducing a new channel
`resultCollected`. This channel is used to signal the payment
lifecycle that an HTLC attempt result is ready to be processed.
The routing package implements authentication+validation of channel
announcements, pruning of the channel graph, path finding within the network,
sending outgoing payments into the network and synchronizing new peers to our
channel graph state.
Installation and Updating
$ go get -u github.com/lightningnetwork/lnd/routing