Use string input instead of filename

[jreina]

I'm not sure how you would want to organize this but I would like to see this library able to take a string and turn it into an image.

If this were to be added, would you want to have an additional property added to the argument object of convert or something else entirely?

The use case is that I don't want to have to save a file in order to render it. I can read from the FS if I want to, or I can pass in a string from a chat message (my current use case), email, etc.