In-place anonymous structs

[Shvandre]

Maybe we should add anonymous structs and messages? Sometimes it is needed to send message only one time - and there is no need to generate abi, docs etc. for it.
Possible syntax

message(0xd53276db) {
    value: Int as coins;
    query_id: Int as uint64;
} my_msg = {query_id: 0}

or even in C-style

message(0xd53276db) {
    value: Int as coins;
    query_id: Int as uint64;
} my_msg = {0, 0}