Compound key support, simply.

* support compound primary keyed table.
* ::new method can accept mass-assignment with hash.
* inserter use Keyspace#write method for batch write.
Add credit where credit is due
Some scripts for convenience
Cleanup and improvements for basic compound key support

In particular, scopes correctly iterate over batches even when there is a
compound key requiring a "next" batch at several levels. Introduce the
Scope#at and Scope#after methods, which may not be an awesome API.
Merge pull request #20 from cequel/simple_compound_keys

Simple compound key support