feat: allow plugins

// in testacular.conf.js
plugins = ['some-plugin']

The 'some-plugin' will be required as a node module, it needs to be DI module.

// some-plugin.js
module.exports = {
  'preprocessor:coffee': ['factory', function(){}]
};

lib/config.js

@@ -131,7 +131,8 @@ var parseConfig = function(configFilePath, cliOptions) {
       type: 'html',
       dir: 'coverage/'
     },
-    loggers: [ constant.CONSOLE_APPENDER ]
+    loggers: [ constant.CONSOLE_APPENDER ],
+    plugins: []
   };
 
   var ADAPTER_DIR = __dirname + '/../adapter';

lib/server.js

@@ -229,17 +229,26 @@ start.$inject = ['injector', 'config', 'launcher', 'emitter', 'preprocess', 'fil
 
 
 exports.start = function(cliOptions, done) {
-  var injector = new di.Injector([
-    ['done', 'value', done || process.exit],
-    ['emitter', 'type', EventEmitter],
-    ['launcher', 'type', Launcher],
-    ['config', 'value', cfg.parseConfig(cliOptions.configFile, cliOptions)],
-    ['preprocess', 'factory', preprocessor.createPreprocessor],
-    ['fileList', 'type', FileList],
-    ['webServer', 'factory', ws.createWebServer],
-    ['reporter', 'factory', reporter.createReporters],
-    ['capturedBrowsers', 'type', browser.Collection]
-  ]);
+  var config = cfg.parseConfig(cliOptions.configFile, cliOptions);
+  var modules = [{
+    logger: ['value', logger],
+    done: ['value', done || process.exit],
+    emitter: ['type', EventEmitter],
+    launcher: ['type', Launcher],
+    config: ['value', config],
+    preprocess: ['factory', preprocessor.createPreprocessor],
+    fileList: ['type', FileList],
+    webServer: ['factory', ws.createWebServer],
+    reporter: ['factory', reporter.createReporters],
+    capturedBrowsers: ['type', browser.Collection]
+  }];
+
+  // register all plugins
+  config.plugins.forEach(function(plugin) {
+    modules.push(require('../plugins/' + plugin));
+  });
+
+  var injector = new di.Injector(modules);
 
   injector.invoke(start);
 };