Adds TypeStatement for declaring new types

[markwpearce]

Adds type newTypeName = <other type> statement, useful for declaring type shorthands.

eg:

type number = float or integer or double

function sum(x as number, y as number) as number
    return x + y
end function

Hovers:

Code Completion:

Validation:

To do:

• Add new CustomType WrappedType class so we can create custom toString() methods for these types
• Update Hovers so it shows the new type name
• Add Scope Validation tests
• Deal with name collisions
• Add documentation