Add configurable config file

* Add ability to recurse up directory tree to find nearest config file
* Add ability to define a custom config path in `package.json` (relative to `package.json`)

Resolves sasstools#47

lib/config.js

@@ -5,22 +5,55 @@ var yaml = require('js-yaml'),
     path = require('path'),
     merge = require('merge');
 
-var defaults = yaml.safeLoad(fs.readFileSync(path.join(__dirname, '/config/sass-lint.yml'), 'utf8')),
-    configPath = path.join(process.cwd(), '/.sass-lint.yml');
+var defaults = yaml.safeLoad(fs.readFileSync(path.join(__dirname, 'config', 'sass-lint.yml'), 'utf8'));
+
+var findFile = function findFile (configPath, filename) {
+  var HOME = process.env.HOME || process.env.HOMEPATH || process.env.USERPROFILE,
+      dirname,
+      parentDirname;
+
+  configPath = configPath || path.join(process.cwd(), filename);
+
+  if (fs.existsSync(configPath)) {
+    return fs.realpathSync(configPath);
+  }
+
+  dirname = path.dirname(configPath);
+  parentDirname = path.dirname(dirname);
+
+  if (dirname === HOME || dirname === parentDirname) {
+    return null;
+  }
+
+  configPath = path.join(parentDirname, filename);
+
+  return findFile(configPath, filename);
+};
 
 module.exports = function (options) {
-  var config = {},
+  var configPath,
+      meta,
+      metaPath,
+      config,
       finalConfig = {};
 
-  finalConfig = defaults;
+  metaPath = findFile(null, 'package.json');
+  meta = require(metaPath);
+
+  if (meta.sasslintConfig) {
+    configPath = path.resolve(path.dirname(metaPath), meta.sasslintConfig);
+  }
+  else {
+    configPath = findFile(null, '.sass-lint.yml');
+  }
 
   if (fs.existsSync(configPath)) {
     config = yaml.safeLoad(fs.readFileSync(configPath, 'utf8'));
-    finalConfig = merge.recursive(finalConfig, config);
+    finalConfig = merge.recursive(defaults, config);
   }
 
   if (options) {
-    finalConfig = merge.recursive(finalConfig, options);
+    finalConfig = merge.recursive(defaults, options);
   }
 
   return finalConfig;