introduce a dedicated Address representation

[williballenthin]

various formats represent addresses in different ways, e.g. native code uses VA while .NET uses tokens.

introduce a class hierarchy for addresses that implement the necessary operations (eq, ord, hash, repr). use these instances for "as long as possible" only at the last moment (in render) turning them into textual representations.

this may require some changes to freeze

[williballenthin]

optimization: may be able to cache Address instances to be yielded by the extractors to reduce GC pressure?