Don't emit a trailng newline in base64-encoded data like 'image/png'

[xl0]

This should address #930

[blink1073]

Thank you!

[kevin-bates]

@xl0 thanks for the pull request and analysis, it all makes sense to me.

My only concern, given the time that a training \n has been in use, is that some applications may be expecting it or will not tolerate its absence gracefully and i wonder if this is something that should be configurable, at least initially.

I'm unable to check the history of that call but I would imagine it's been around since prior to python 3.6.

This configurable could be something akin to the message debug option where, iirc, it isn't a configurable trait. That would at least give intolerant applications a way forward.

(Sorry, I've access to only my phone at the moment but wanted to raise this topic.)

[blink1073]

I would say anyone consuming these values would have most likely called strip() on them, which would still work.