add a to_b64 function

[mchant]

Would it be useful if I create a PR for a to_b64 function? It's pretty much a copy of the write_image function, but returns a b64 string rather than write to a file.

[andrei-ng]

Hi @mchant ,

Isn't to_html or to_inline_html sufficient for this use-case?

[mchant]

Thanks for the reply, @andrei-ng. Those functions return html that makes a call to plotly. If someone just wants data for a picture, they can use this tag <img src="data:image/jpeg;base64,{b64_string_here}"> and pass in the string. This also returns a fairly consistent data length no matter how much data is used in the plot. In an HTTP API environment, this makes a more predictable load time because the data returned is not dependent on the length of x and y.

[andrei-ng]

Hi @mchant. Thanks for the clarification. Yes, please submit a PR and I will merge it in. If you need to use an external crate to achieve this, I think it is better to put it behind a feature flag.

[mchant]

Hi, @andrei-ng , it's in PR #251