Set function names from assignment expressions

Based on http://www.2ality.com/2015/09/function-names-es6.html.

packages/babel-plugin-transform-es2015-function-name/test/fixtures/function-name/function-assignment/actual.js

@@ -0,0 +1,13 @@
+var foo;
+foo = function() {
+};
+
+var baz;
+baz = function() {
+  baz();
+};
+baz = 12;
+
+bar = function() {
+  bar();
+};

packages/babel-plugin-transform-es2015-function-name/test/fixtures/function-name/function-assignment/expected.js

@@ -0,0 +1,22 @@
+var foo;
+foo = function foo() {};
+
+var _baz;
+_baz = function baz() {
+  _baz();
+};
+_baz = 12;
+
+bar = function (_bar) {
+  function bar() {
+    return _bar.apply(this, arguments);
+  }
+
+  bar.toString = function () {
+    return _bar.toString();
+  };
+
+  return bar;
+}(function () {
+  bar();
+});