Add StreamedJsonArray wrapper

Default EntityEncoder for Stream[F, A] works that all As are streamed as invalid JSON:

{"name": "Bob"}{"name": "Fred"}

instead of

[{"name": "Bob"},{"name": "Fred"}]

I believe that this behavior is slightly confusing, but nevertheless valid. However, we can add auxiliary wrapper class and corresponding encoder to it. Example implementation: https://gist.github.com/andimiller/671d5bfdfbf9ef1411522ca9c88a369c

[armanbilge]

@SoTeKie sure, it’s yours if you want 😃

[SoTeKie]

Hello again, sadly for personal reasons I won’t actually have the time to work on this 😦 Sorry for any inconvenience caused by this.