This commit moves the creations of hop and htlcAdd message from
`createNewPaymentAttempt` to `sendPaymentAttempt` to clean up the code
and further pave the way to decomposite the lifecycle.
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