v1.2.0

• Support storing of a custom per-isolate data structure (Napi::Env::GetInstanceData and Napi::Env::SetInstanceData)
• Specify the memory ownership rules for Buffer
• Support returning references to nested objects
• Fix #16, global and static members can be noexcept
• Fix a minor memory leak when calling a method with incorrect number of arguments
• More meaningful exceptions for constructors to aid debugging