code: function md5(files) {
  		var hash = crypto.createHash('md5');
  		_.each(files, function(file) {
  			if (!isExternal(file))
  				hash.update(grunt.file.read(file), 'utf-8');
  		});
      	return hash.digest('hex');
  	}
docs: Computes an MD5 digest of given files.
  
  @param  array files
  @return MD5 hash (hex-encoded)