Currently execute_batch always return nil.

1. Would it be better to return the result of the last statement instead?
2. Would it make sense to accept a list of statements as well? For example:

db.execute_batch [
  "PRAGMA empty_result_callbacks=1",
  "CREATE TABLE t1(a,b)",
  "CREATE INDEX t1i3 ON t1(a,b)",
  "INSERT INTO t1 VALUES(1, 2)",
  "SELECT * FROM t1",
]

or simply db.execute [...]?