Make parser support multi-line via `\r\n`

This makes the library feel more like a typical parsing stream.  The main changes are to include the ability to parse the "string literals" as part of imap-parser and support splitting multiple lines out automatically using `\r\n`.

It also renames the `line` event to `data` as this would allow it to make more sense as a parsing stream in the future.  One `data` event is emitted for each line.

Since it handles multiple lines and string literals internally, you can just `.pipe` the connection stream to it in order to get a parsed version of the connection stream.

I'd love it if @andris9 could review this for whether it would still work with [inbox](https://github.com/andris9/inbox/pull/24)