Upgrade to latest preact and to hooks instead of classes

[joeldenning]

This would likely reduce the library size pretty drastically, and is also the norm now for react projects. At the time I authored this, react had released hooks but preact had not.

[frehner]

I was also thinking it may be helpful to add in a small header in the output bundle with the version number, just so we can more easily debug those with those CDN issues and stuff

[joeldenning]

👍 agreed

[robmosca]

This is addressed in #94, @joeldenning