Adjusting date time text to match image size

[ZachHoppinen]

Hello,

Feel free to close if this isn't helpful but when I use this great package with large xarray dataarrays the date text in the corner get very small and illegible. This push:

• Sets an initial text size of 6 pt
• Checks if the resulting bounding box will be 10% of image width
• If it is smaller it increments to the next larger font size until the date time text fills in 10% of image

Credit to this slack exchange answer: https://stackoverflow.com/questions/4902198/pil-how-to-scale-text-size-in-relation-to-the-size-of-the-image

One weird thing I found was the background box was too short vertically after these changes so I added a 1.6x multiplier to the height to make the text work but I suspect I may just be missing something there.

Cheers! Zach

[ZachHoppinen]

Just noticed this may resolve #18 to some extent as well.

[gjoseph92]

@ZachHoppinen I'll leave this for you to test out on your data, but I think it's good to go, so once you confirm I'll merge and cut a release!

[ZachHoppinen]

@gjoseph92 Just ran this on my data for a few different font sizes and fractions and it looks awesome now! Thanks for cleaning that all up and for this super cool project!

[gjoseph92]

Great to hear! Thanks for the contribution and figuring out the core change!