Issue title: saving intermediate checkpoint
 Issue body: HI, 
Is your code saving the intermediate checkpoints ? if no how to do I add the code for it ?
 Comments: 
 Comment 0: @JiteshPshah yes, your can modify this parameter in  [/ctpn/text.yml](https://github.com/eragonruan/text-detection-ctpn/blob/5d091787c9ba2e0c5da919341a9fe11117cceab2/ctpn/text.yml#L17), currently, i save the model every 1k steps
 Comment 1: @eragonruan  Thanks Buddy ....
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