This branch adds an implementation of a singly-linked mutable FIFO
`Stack`and a singly-linked lock-free FIFO `TransferStack` in
`cordyceps::stack`.

A `Stack` is just your traditional FIFO stack structure.
`TransferStack` is a bit more interesting --- it's a simplification of
the traditional lock-free Treiber stack wher all elements are popped
into a new mutable `Stack` in a single atomic operation. This avoids the
ABA problem issues common with naive Treiber stack implementations. It's
intended primarily for use in a `mimalloc`-style sharded per-core memory
allocator.

Closes #137

Signed-off-by: Eliza Weisman <eliza@elizaswebsite>