feat(identity): initial commit of function

src/_identity.scss

@@ -0,0 +1,16 @@
+@import 'head';
+
+/// A function that does nothing but return the parameter supplied to it. Good
+/// as a default or placeholder function.
+///
+/// @group function
+/// @return {bool} true
+///
+/// @example scss - indentity
+///
+///   $is-one: identity(1);
+///   @debug $is-one; //=> 1
+
+@function identity($args...) {
+  @return head($args);
+}

test/_identity.spec.scss

@@ -0,0 +1,10 @@
+@import 'true';
+@import '../src/identity';
+
+@include describe('identity [function]') {
+    @include it('returns its first argument') {
+        @include assert-equal(identity(null), null);
+        @include assert-equal(identity('foo'), 'foo');
+        @include assert-equal(identity('foo', 'bar'), 'foo');
+    }
+}