Enable Structure Inheritance from other Structures

This would be an useful feature for those who are forced to use abstract classes for entities as structures can't inherit.

Example:

```vb
Public MustInherit Structure BaseBall
Public MustOverride ReadOnly Property Cost As Integer
Public MustOverride ReadOnly Property CatchRate As Integer
Public MustOverride ReadOnly Property Name As String
End Structure

Public Structure GreatBall
Inherits BaseBall

Public Overrides ReadOnly Property Cost As Integer
Get
Return 5
End Get
End Property

Public Overrides ReadOnly Property CatchRate As Integer
Get
Return 200
End Get
End Property

Public Overrides ReadOnly Property Name As String
Get
Return "Great Ball"
End Get
End Property
End Structure
```