The route-builder checks the liquidity bounds of each route one at a
time. Every route that satisfy the contraints is recorded in the
uncertainty network and produces an HTLC burden on the channels it uses,
so that the following routes cannot count on the same liquidity twice.
Routes contain only routing information and the payment they're linked
to can be obtained through the payment_hash. We remove the dependency of
route building routines from the payment itself. In order to make
plain payment information available we define a payment_info structure.
- use switch case over all possible WIRE_* errors,
- remove the virtual machine for routefail, use a simple two step
solution: 1. update the gossip and 2. handle error cases
Routebuilder constitute the module that builds the routes we try in the
payment. The public API is simply `get_routes`, it replaces the similar
interface for pay_flows.
