Created by: xjqbest

• add save with prefix
• test=develop

usage:

fleet.save_model("./model0",)
fleet.save_model("./model0", mode=0)

fleet.save_one_table(0, "./model1")
fleet.save_one_table(0, "./model1", mode=0)

# if you set prefix, the saved part has prefix:  "part-hahaha-"
# the save path should contain table id like 000, 001.etc.
fleet.save_one_table(0, "./model1/000", prefix="hahaha")
fleet.save_one_table(1, "./model1/000", mode=0, prefix="hehehe")

fleet.load_model("./model0")
fleet.load_model("./model0", mode=0)

fleet.load_one_table("./model0")
fleet.load_one_table("./model0", mode=0)

note: load model or load one table does not support prefix, which means it can not load models with prefix.