Lorm

[NEW] support "not in" filter
db.pet.filter(id__ni=[1,2])

[FIX] fix slice bug

[NEW] compatible python3

[DEL] MysqlPool.__len__

[NEW] MysqlConnection.select_db
[NEW] MysqlConnection.dup(**kwargs)

[NEW] support negative slice index. e.g. c.pets[-1:]
[NEW] add 'values', 'flat' row-style
[FIX] using count() implements __len__()
[FIX] optimize count() and exists()