Move internal modules to “internal” folder.

.internal/baseFunctions.js

@@ -0,0 +1,17 @@
+import arrayFilter from './.internal/arrayFilter.js';
+import isFunction from './isFunction.js';
+
+/**
+ * The base implementation of `functions` which creates an array of
+ * `object` function property names filtered from `props`.
+ *
+ * @private
+ * @param {Object} object The object to inspect.
+ * @param {Array} props The property names to filter.
+ * @returns {Array} Returns the function names.
+ */
+function baseFunctions(object, props) {
+  return arrayFilter(props, key => isFunction(object[key]));
+}
+
+export default baseFunctions;