make evm.logs() useful

[snd]

right now it just returns a vec of () per event. make it return actual events. also make the filter optional for the case where the user simply wants all events.

[snd]

i started working on this over here: https://github.com/paritytech/sol-rs/pull/14

thinking of the following API at the moment:

1) to get all logs:

pub fn raw_logs(&self) -> Vec<ethabi::RawLog>

2) to get logs for a specific event:

pub fn logs<T: EventTrait>(&self, event: T) -> Vec<T::Log>

used like this:

let deposit_logs = evm.logs(foreign_bridge.events().deposit());

2 is currently not possible because the EventTrait doesn't exist. currently events created by ethabi derive are structs that implement the same methods but don't share a trait: https://gist.github.com/snd/8dad886c6acdf057a18e2c29b6255c48#file-foreign_bridge-rs-L86 the events created by ethabi derive could all implement the following trait which would make 2 possible:

pub trait EventTrait {
    type Log;

    fn parse_log(&self, log: ethabi::RawLog) -> ethabi::Result<Self::Log>;
    fn create_filter(&self) -> ethabi::TopicFilter;
}

i don't like the name EventTrait. ethabi::Event is already taken by the event struct.

i'd love your feedback on this

[snd]

relevant diff https://github.com/paritytech/sol-rs/compare/snd-issue-30...snd-logs