A pull based event channel, with events stored in a ring buffer, meant to be used as a resource in [specs].

Example usage

```rust extern crate shrev;

use shrev::EventChannel;

[derive(Clone, Debug, PartialEq, Eq)]

pub struct TestEvent { data: u32, }

fn main() { let mut channel = EventChannel::new();

channel.drain_vec_write(&mut vec![TestEvent { data: 1 }, TestEvent { data: 2 }]);

let mut reader_id = channel.register_reader();

// Should be empty, because reader was created after the write
assert_eq!(
    Vec::<TestEvent>::default(),
    channel.read(&mut reader_id).cloned().collect::<Vec<_>>()
);

// Should have data, as a second write was done
channel.single_write(TestEvent { data: 5 });

assert_eq!(
    vec![TestEvent { data: 5 }],
    channel.read(&mut reader_id).cloned().collect::<Vec<_>>()
);

// We can also just send in an iterator.
channel.iter_write(
    [TestEvent { data: 8 }, TestEvent { data: 9 }]
        .iter()
        .cloned(),
);

assert_eq!(
    vec![TestEvent { data: 8 }, TestEvent { data: 9 }],
    channel.read(&mut reader_id).cloned().collect::<Vec<_>>()
);

} ```