Add example config files and source codes

[ruimashita]

In orde to easily start blueoil for new user, we have tutorial documentations. Current tutorial at documentation site have the chapter of generating config, but it occur problems.

• The config specification changes often in our current stage, It takes cost to need to change not only config specification document but also tutorial documents. Idealy, the tutorials need to assure to work well to not lost new user, but currently, there are no test.
• Can't grasp how to use blueoil from source code, Need to read carefully the tutorials.

To resolve these problems, create examples directories, and add config file or some codes to do tutorials like theses.

examples/classification/config.yml examples/object_detection/config.yml examples/object_detection/prepare_dataset.py

[patrick-su]

@ruimashita seems like this can be closed?