Switch per-build versioning convention.

We switched to having Jenkins overwrite the value of the __build__
variable because that works better when a build installs another
source distribution.
Use bintrees to implement sorted sets.
Add stub functions for sorted sets
Revert use of bintrees; it's not a great fit.
Improve sorted set:

 - Keep sorted list of (score, member) pairs.
 - Keep dictionary of member to score

Still uses O(N) list insert and removal operations.
More Pythonic container interface.
Implement zadd.

Fix return value of insert() to match documentation.
Implement zcard
Implement ZINCRBY
Implement zrange
Implement zrem
Implement ZSCORE
Implement zrevrange
Implement ZRANK
Implement ZCOUNT
Implement ZRANGEBYSCORE
Implement ZREVRANK
Implement ZREVRANGEBYSCORE
Implement ZREMRANGEBYRANK and ZREMRANGEBYSCORE
Implement ZUNIONSTORE