Extract internal lock-free data structures as public APIs

[nicowilliams]

• lock-free queue (used in the slotlist TSV implementation)
• array/rope (ditto) (this is a list of ever-larger array chunks so array indexing is logarithmic and fast)
• add a bitmask rope flavor of array/rope for allocation of indices into a thread-local array where the indices correspond to TSVs (and not just TSVs, but any other lock-free data structures based on hazard pointers, and any other thread-local caches of anything)
• add a file descriptor table like data structure, but generic (we could use this to have a set of named TSVs, where the names can be things like file paths)

The array/rope would be nice for file descriptor table like data structures. We could use all of this for getting down to one pthread_key_t for the whole thing, where the one key drives thread exit time cleanup for all the things.