IPC RPC deriving for traits

[NikVolf]

#[derive(Ipc)]
trait DBNotify {
    fn notify(&self, a: u64, b: u64) -> bool;
}

so that above become possible

needed for pub/sub IPC scenarios

goes after #1584

[rphmeier]

travis failure is legitimate

[coveralls]

Changes Unknown when pulling c33788f on ipc-trait-interface into * on master*.

[gavofyork]

needs resolving.

[NikVolf]

@gavofyork rebasing? - done
though i had to resolve the same conflicts twice because of the commits squashing again

[coveralls]

Coverage increased (+0.02%) to 76.644% when pulling c60e02d on ipc-trait-interface into 6c20506 on master.