Replaces numeric status codes with a canonical set of Status objects,
each with a short name and description.
Bindings with more specific errors (e.g., timeouts) return additional
statuses.

This changes the default output from messages like:

   [UPDATE], Return=0, 511

To:

   [UPDATE], Return=OK, 511

This will ensure record ordering my the primary key.

Now properly enforcing a scan of the given number of documents in the
scan operation using the LIMIT modifier in the cached statement.

Fixes #171.

Fixes #438

JDBC scans did not instruct the driver to use a specific fetchsize,
resulting in most cases in an OOM; add support for setting fetchsize.

Also add support for disabling autocommit on the JDBC connections,
mostly because Postgres for example doesn't support setting fetchsize
without disabling autocommit.