1. Remove unused  arguments.
2. Refine doc.
3. Change 'device' to 'use_gpu'.

1. Remove illustration of arguments.
2. Make inference support for more format input.

1. Add document.
2. Add arguments for saving model and init model.
3. Refine inference.py and eval.py.
4. Make ctc_reader.py support for custom data.

2. Add inference script
3. Add load model script
4. Add some functions into ctc_reader