Framework

1. Add config file global.cfg, a mapping from picture label to number
   which will be used in model.
2. Add script png-csv-test.py, convert picture from png to vector.
3. Add script png-csv-train.py, convert picture from png to vector
   and extract the labels in it.
4. Add funciton load_config to module_io, read in config from config
   file.
5. Add function load_label_number_dict to module_io, read in the label
   mapping from config file, the mapping is from lable to number.
6. Add function load_number_label_dict to module_io, read in the label
   mapping from config file, the mapping is from number to label.