Deprecate "autoload.exclude-from-files" support

Added:
- Warning against using "autoload.exclude-from-files" and to use "extra.exclude…" instead

src/ExcludeFilePlugin.php

@@ -31,6 +31,11 @@ class ExcludeFilePlugin implements
      */
     private $composer;
 
+    /**
+     * @var IOInterface
+     */
+    private $io;
+
     /**
      * Apply plugin modifications to Composer.
      *
@@ -41,6 +46,7 @@ class ExcludeFilePlugin implements
     public function activate(Composer $composer, IOInterface $io)
     {
         $this->composer = $composer;
+        $this->io       = $io;
     }
 
     /**
@@ -182,6 +188,7 @@ private function getExcludedFiles(PackageInterface $package)
 
         // Skip misconfigured or empty packages
         if (isset($autoload[$type]) && is_array($autoload[$type])) {
+            $this->io->writeError('<warning>Using the "'.$type.'" property from "autoload" is deprecated and will be removed in mcaskill/composer-exclude-files v2.0. Use the property from "extra" instead.</warning>');
             return $autoload[$type];
         }