Created by: ceci3

1. add median stop

example:

from paddleslim.nas import SANAS
from paddleslim.nas.early_stop import MedianStop


steps = 10
epochs = 7

config = [('MobileNetV2Space')]
sanas = SANAS(config, server_addr=("", 8732), save_checkpoint=None)

### add for early stop
earlystop = MedianStop(sanas, 2)

for step in range(steps):
    archs = sanas.next_archs()[0]
    for epoch in range(epochs):
        for data in train_reader():
            loss = archs(data)

        for data in test_reader():
            loss = archs(data)
        avg_cost = np.mean(loss)

        ### add for early stop
        status = earlystop.get_status(step, avg_cost, epochs)
        if status == 'BAD':
            break;

    sanas.reward(avg_cost)