[RFC] [PATCH] Provide the ability to write the frame unwinder in Python

[Alexander Smundak]

> Regarding the result of an unwinder/sniffer,
> If I approach this from the point of view of what's
> easy to explain, it feels like the result of an Unwinder
> is a Frame.
It is logical, but that's not what GDB core expects from the unwinder.
I hesitate to have Python frame unwinder API differ too much from
 the underlying GDB core API.

> Would it make sense to speak of an Unwinder taking
> an EphemeralFrame as input and returning a Frame as output?
Existing gdb.Frame interface wraps GDB core's `frame_info',
providing read-only capability and no instance construction.
An object returned by a Python unwinder is quite different.