Merge branch 'v4' of https://github.com/twbs/derpstrap into v4

Conflicts:
	docs/components/helpers.md
	scss/_utilities.scss

scss/_utilities.scss

@@ -46,12 +46,6 @@
   z-index: $zindex-navbar-fixed;
 }
 
-
-// Toggling content
-.show {
-  display: block !important;
-}
-
 // Always hide an element with the `hidden` HTML attribute (from PureCSS).
 [hidden] {
   display: none !important;
@@ -66,15 +60,6 @@
 }
 
 
-// Hide from screenreaders and browsers
-//
-// Credit: HTML5 Boilerplate
-.hidden {
-  display: none !important;
-  visibility: hidden !important;
-}
-
-
 // For Affix plugin
 .affix {
   position: fixed;