added a script to instantiate DbAccess object.
use the dbaccess.php script in tests.
added a simple test for join table.
moved join logic to SqlBuilder.
QueryObject to contain query type, and SqlBuilder uses the type
to determine which sql to build.
pass queryObject to DbAccess to execute sql query.
fixed Query's tests; Query now only takes care of QueryObject, hece made the test difficult.
renamed member properties to reflect new class name.
added dbConnect to serialize; what if pdo is an array; added more comments.
removed building sql. should be done in DbAccess.
removed test since Query does not throw Exception any more.
added more comments.