code: public static SnapshotResult makeSnapshot (String feedId, DataSource dataSource) {
          JdbcGtfsSnapshotter snapshotter = new JdbcGtfsSnapshotter(feedId, dataSource);
          SnapshotResult result = snapshotter.copyTables();
          return result;
      }
docs: Copy all tables for a given feed ID (schema namespace) into a new namespace in the given JDBC DataSource.
  
  The resulting snapshot from this operation is intended to be edited, so there are a handful of changes made to
  the newly copied tables:
  1. The tables' id column has been modified to be auto-incrementing.
  2. Primary keys may be added to certain columns/tables.
  3. Additional editor-specific columns are added to certain tables.
  @param feedId        feed ID (schema namespace) to copy from
  @param dataSource    JDBC connection to existing database
  @return              FIXME should this be a separate SnapshotResult object?