Improve naming of `hill-device-min` and `hill-device-max` mixins

[Vaddo]

I have the following breakpoint configuration:

$hill-layout-breakpoints: (
    small:  480px,
    medium: 640px,
    large:  1200px
);

At the moment if you use the hill-device-min mixin like this:

@include hill-device-min(medium) {
  ... some scss here
}

it outputs only code for large device like this:

@media (min-width: 641px) {
  ... output css here
}

I expect css output for medium and large devices. Maybe mixin name should be more specific like hill-device-upper or hill-device-larger?