Include support to COCO dataset format

[chanfr]

No description provided.

[vinay0410]

Hi @chanfr ,
This is regarding parsing JSON files using COCO dataset, and since we have agreed on using rapidjson. I would like to mention that rapidjson is already a dependency in DetectionSuite.

So, we can continue to write code using rapidjson, or if neccesary, we can also remove this external dependency.
Since it is header only library, it can be directly used in our code without the need to be installed. This way we can maintain its version compatibility since users might have different versions installed.

I had to update my rapidjson version in ubuntu to fix some errors.

Which way do you think is the best way to go ?