Non-Escapable Types proposal

Briefly, non-escapable types are types that cannot "escape" the local
execution context.  These types can also participate in extended
lifetime dependency constraints.  This enables compile-time lifetime
enforcement for values that contain pointers into other values.  This
makes it possible to implement containers that require no runtime
lifetime management of their iterators or slice objects.

In particular, this is a foundational technology for BufferView.

Author: tbkka