doc: tutorial nice highlighting for error_code values in network stuff
doc: tutorial nice highlighting for error_code values in network stuff

libtetcoin/libtetcoin-consensus,libmetrocoin/libmetrocoin-consensus,swansontec/libbitcoin,libtetcoin/libtetcoin-consensus,GroestlCoin/libgroestlcoin,kaostao/libbitcoin,swansontec/libbitcoin,kaostao/libbitcoin,BWallet/libbitcoin,libtetcoin/libtetcoin-consensus,kaostao/libbitcoin,libmetrocoin/libmetrocoin-consensus,BWallet/libbitcoin,Airbitz/libbitcoin,kaostao/libbitcoin,Airbitz/libbitcoin,swansontec/libbitcoin,libtetcoin/libtetcoin-consensus,GroestlCoin/libgroestlcoin,BWallet/libbitcoin,GroestlCoin/libgroestlcoin,BWallet/libbitcoin,libtetcoin/libtetcoin-consensus,Airbitz/libbitcoin,libmetrocoin/libmetrocoin-consensus,libmetrocoin/libmetrocoin-consensus,swansontec/libbitcoin,GroestlCoin/libgroestlcoin,Airbitz/libbitcoin,libmetrocoin/libmetrocoin-consensus