SSE server using Actix Web

Use
```rust
use sseserver::{ssestart};
[actix_rt::main]
async fn main() -> std::result::Result<(), std::io::Error> {
ssestart("*".toowned()).await
}
```
- the only param is the origin you want to allow - wildcard for all
- the PORT needs to passed in as an environment variable
Example
- run
make
and make client
in two different terminal windows to run example
Example
- https://sse-demo.mynextlevel.dev