Spy API?

There is no nice way to spy just one function of an object.
```vbscript
aa = {
   someFun: function()
     ? "doing something"
   end function
}

' what about?

_brs_.spyFunction(aa, "someFun")

aa.someFun("hey") ' does nothing
aa.someFun.called ' true
aa.someFun.calledWith ' ["hey"]
aa.someFun.calledTimes ' 1
```
