Shorten share URLs by default

[laundmo]

Currently, the URLs when trying to share a formatted file can get VERY long. This is suboptimal for sharing the links on sites or services that do not support hiding the links in any way, like Discord which is what the psf/black team now uses to communicate. (I've even seen a link exceed the 2000 character per message limit on Discord)

I propose shortening the URLs by default, possibly even just using a existing link shortener.