Provide a mixin for equal-width columns

[lacorde]

With _grid.scss, Bootstrap provides many useful mixins for grid integration such as make-col() or make-row().

But there is no mixin for basic equal-width flexbox columns such as .col-sm, .col-md...
Having the following would be great:

@mixin make-col-equal() {
  flex: 1 0 0%;
}

Which could be then included according to breakpoint:

@include media-breakpoint-up(sm) {
  @include make-col-equal();
}

What do you guys think ?