Responsive display utilities

This explores adding responsive display utilities, replacing the static inline, inline-block, and block options we have currently. The twist here though is that the lowest breakpoint doesn't have a breakpoint abbreviation in the class name.

Here's an example of what I mean with just the display: none utility:

/* Same as `.d-xs-none`, but without the `-xs` part */
.d-none { display: none !important; }

@media (min-width: 576px) {
  .d-sm-none { display: none !important; }
}

@media (min-width: 768px) {
  .d-md-none { display: none !important; }
}

@media (min-width: 992px) {
  .d-lg-none { display: none !important; }
}

@media (min-width: 1200px) {
  .d-xl-none { display: none !important; }
}

I'm exploring this since the lack of xs could make it an easier transition to v4 for those who used the v3 utilities. Plus it's a bit more accurate to what's happening in the compiled CSS since there's no media query around those styles.

Thoughts?