Alex Miller propose to also support unordered key-value store in SRFI-167.

To apply this proposal, I will need to:

- rename from 'Ordered Key-Value Store' to 'Key-Value Store'

- make 'okvs-range' optional

- make 'okvs-prefix' optional

Such databases include:

- Memcached

- RIAK

- GNU GDBM

What do you think?