Enable serveClient() accept second parameters and forward it to view engine

Make it similar to Express's render method:
    
    res.render('main', [locals]);

In socketstream:

    res.serveClient('main', {
      title : 'main',
      version : '1.0',
      ...
    });

Corresponding view engine wrappers need to be modified to enable this feature.  For example, in ss-jade/wrapper.js, compile function needs to be modified. 

    compile: function(path, options, cb) {

      // locals now can be accessed by options.locals. 
      var locals = (options && options.locals) ? options.locals : {};
      ...

      var output = parser(locals);
      cb(output);
    }