.img-fluid Should not apply display:block by default

[arctic-ice-cool]

The .img-fluid class applies display: block; styling by default. This is a completely different & additional behaviour to what .img-fluid is meant to do.

Shouldn't .img-block be a seperate class?

[mdo]

Agreed that display: block is unnecessary for the max-width and height: auto to have an affect—see https://jsbin.com/tefukez/. I'll remove that in Alpha 5.

However, I won't be adding img-block—there are other display utils for that.