Add support and docs for color input

scss/forms/_form-control.scss

@@ -110,3 +110,8 @@
   line-height: $input-line-height-lg;
   @include border-radius($input-border-radius-lg);
 }
+
+.form-control-color {
+  max-width: 3rem;
+  padding: ($input-padding-y / 2) ($input-padding-x / 2);
+}