Update java.jdbc to 0.3.0.

java.jdbc 0.3.0 contains breaking changes: DDL functionality has
been moved to java-jdbc/dsl and API has changed. This commit
modifies ragtime to work with java.jdbc 0.3.0 and to use DDL
functionality from java-jdbc/dsl 0.1. Ragtime no longer works with
java.jdbc 0.2.3 after this commit. Fixes issue #23.