add inference example, some small improvements in training code

1. add inference example
2. some small improvements in training code

simple multi character image captcha solving using CNN model

release/v1.0

update README for CNN model

input_data for multi labels

v0.4

run log of conv_captcha

CNN-single-label-captcha

1. 0-9 的数字，识别正确率 99%
2. 验证码字符集，从 0-9 的数字扩展至 数字+英文小写字母。正确率 80%

tensorboard support

v0.2

image for tensorboard

single captcha with softmax layer only

1 个字符，1 个 softmax 层，正确率 92%
https://zhuanlan.zhihu.com/p/25606916