* Fix#2612: adjust readable trait to allow try_peek
Our implementation for Readable was inconsistent.
We had a try_unchecked variant for read but not for peek.
This resolves that by making a breaking change to the
Readable interface.
* fix doctests too
* Fix generation race condition with sync storage
* Document GenerationalPointer
* check generation before recycling generational box
* fix clippy
* make race_condition_regression test panic if it fails
Jonathan Kelley