added debugging opportunity

Author: mightyaleksey

package.json

@@ -7,6 +7,7 @@
     "node": ">=0.12"
   },
   "dependencies": {
+    "debug": "^2.2.0",
     "lodash.assign": "^3.2.0",
     "lodash.identity": "^3.0.0",
     "lodash.isarray": "^3.0.4",

src/index.js

@@ -1,3 +1,4 @@
+import debug from 'debug';
 import hook from './hook';
 import { readFileSync } from 'fs';
 import { dirname, sep, relative, resolve } from 'path';
@@ -12,6 +13,9 @@ import LocalByDefault from 'postcss-modules-local-by-default';
 import Scope from 'postcss-modules-scope';
 import Parser from './parser';
 
+const debugFetch = debug('css-modules:fetch');
+const debugSetup = debug('css-modules:setup');
+
 // cache
 let importNr = 0;
 let tokensByFile = {};
@@ -35,6 +39,7 @@ let rootDir = process.cwd();
  * @param  {array}    opts.extensions
  */
 export default function setup(opts = {}) {
+  debugSetup(opts);
   // clearing cache
   importNr = 0;
   tokensByFile = {};
@@ -96,6 +101,7 @@ function fetch(_to, _from, _trace) {
     return tokens;
   }
 
+  debugFetch(filename);
   const rootRelativePath = sep + relative(rootDir, filename);
   const CSSSource = preProcess(readFileSync(filename, 'utf8'), filename);