support typedef syntax in domain

[renzibei]

Hello, this library is awesome!

I noticed that there is no support for typedef syntax in Domain at this stage.

There are a few scenarios where typedef maybe very useful, for example

When we want to represent the following C++ type

typedef vector<StructA> StructAVec;

It will be useful if we can implement this feature in the domain like:

typedef StructA[] StructAVec;

or

struct StructAVec: StructA[];

Thanks a lot!