fix(deepobject): support nested objects in deepObject arrays

[adrianbrad]

Fixes unmarshaling of deepObject-encoded arrays containing nested objects. Previously, the code only handled array elements with simple string values, but failed when array elements were objects with multiple fields.

For : items[0][name]=first&items[0][value]=value1&items[1][name]=second&items[1][value]=value
The object sshould unmarshal to:

[]Item{
      {Name: "first", Value: "value1"},
      {Name: "second", Value: "value2"},
  }

Before this fix, unmarshaling such structures would fail. Now it correctly reconstructs the nested object array.

[mromaszewicz]

Thanks!