In this commit, we export the ReadElements and WriteElements functions.
We do this as exporting these functions makes it possible for outside
packages to define serializations which use the BOLT 1.0 wire format.
This commit fixes a diversion from the way the UpdateAddHTLC message is
defined within the specification. We had the HTLC expiry value in the
wrong place on the wire, which meant that we couldn’t parse the
messages as sent by the other LN implementations.
In this commit BOLT#4 specification message have been added to the
lnwire package. This messsage is needed in order to notify payment
sender that forwarding node unable to parse the onion blob.
