SSE Client

EventSource implementation in Rust to handle streams of Server-Sent Events. It handles connections, redirections, retries and message parsing.

To know more about SSE: Standard | EventSource interface

Example:

```rust extern crate sseclient; use sseclient::EventSource;

let event_source = EventSource::new("http://event-stream-address/sub").unwrap();

eventsource.onmessage(|message| { println!("New message event {:?}", message); });

eventsource.addevent_listener("error", |error| { println!("Error {:?}", error); });

```