Fields without colon gets ignored

According to [WHATWG](https://html.spec.whatwg.org/multipage/server-sent-events.html#dispatchMessage),

The following stream fires two events:
```
data

data
data

data:
```

The first block fires events with the data set to the empty string, as would the last block if it was followed by a blank line. The middle block fires an event with the data set to a single newline character. The last block is discarded because it is not followed by a blank line.

----

But when using the library, no events are fired.
Also what is `ServerSentEventMessage.comment` since comments are not processed and ignored by the library?

Start with the library's Server-Sent Events parsing entry point and compare its handling of fields without colons against the linked WHATWG dispatchMessage specification. Reproduce the supplied event stream, then verify whether empty-data events are emitted and clarify the intended behavior of ServerSentEventMessage.comment.

Written by the indexing model from the issue text.