Iterator-based parser

[elpiel]

This idea was mentioned in #9 and will greatly improve the usability of the crate by providing an iterator-based parser that will parse new messages from e.g. streamed/received bytes when \r\n ending is present.

• Extend with bytes (similar to Iterator::chain)
• Extend with a single byte (optional)
• try_next() try to parse the currently collected bytes (by searching for an ending - \r\n)

Enhancements:

• Track both the ending \r\n but also the start of a message ! (for AIS messages) or $ (for all other) in the iterator.