This commit removes the `peerport` and `rpcport` config options and
adds `listen`, `rpclisten`, and `restlisten` options to allow setting
one or multiple interfaces to listen on for incoming connections.
It also adds a `nolisten` option to allow disabling the listener for
incoming peer connections.
This commit factors out the btcd and ltcd options into their own sections
similar to neutrino, and adds a bitcoind section as well. Now, you specify
node options similarly to:
--ltcd.rpchost=...
or
--btcd.rpcuser=...
or
--bitcoind.zmqpath=...
For Bitcoin, you specify an alternate back-end to btcd as follows:
--bitcoin.node=bitcoind
or
--bitcoin.node=neutrino
You can also specify the default option:
--bitcoin.node=btcd
For Litecoin, only `btcd` mode is valid, and corresponds to the `ltcd`
section. For example:
--litecoin.node=btcd
--ltcd.rpchost=...
The new code also attempts to read the correct options and auth info
from bitcoin.conf just as it does from btcd.conf/ltcd.conf.
