Recursive merge function
``` javascript
function merge (a, b) {
  for (var k in b) {
    try {
      if ( a[k].constructor == Object ) {
        a[k] = merge(a[k], b[k]);
      } else {
        a[k] = b[k];
      }
    } catch(e) {
      a[k] = b[k];
    }
  }
  return a;
}
```

Supports overwriting this.locals variables in subsequent this.render calls
