Allow adding html elements as tooltip content

Can now pass HTMLElement and jQuery objects to the tooltip content option.
Added tests as well. Hopefully those look right.

Pretty much just changed the conditions that are checked for the contentOption variable. I put some of the conditions on separate lines because I thought it increased readability. So if someone could look at the formatting and scold me if I did it wrong, that would be great.
This comparison looks questionable. Not sure about a better way to test this. Maybe `domEqual` can be used here. Also applies to the `equal` call below.