major API changes to be compatible with ForestDB changes

these changes are all around the new support for multiple
key value stores within a single database file

Previously:

	db, err := Open("test", nil)
        if err != nil {
                t.Fatal(err)
        }
	defer db.Close()

Now:

	dbfile, err := Open("test", nil)
	if err != nil {
		t.Fatal(err)
	}
	defer dbfile.Close()

	kvstore, err := dbfile.OpenKVStoreDefault(nil)
	if err != nil {
		t.Fatal(err)
	}
	defer kvstore.Close()