Adding 299x299 broden dataset (for inception_v3, nasnet, pnasnet, nasnet, etc.)

Hi, how much work would it be to create a 299 version of the broden dataset (to complement the existing 224, 227, 384)? I was hoping it would be as easy as adding a few lines to the `makebroden.sh` script but I'm not sure (due to the annotations making things a little more complicated, and I don't know what joingseg does).

If someone is able to provide a quick explanation of what steps to take, I would be happy to do them myself, and then make PR if it would be helpful for others. Quite a few popular models use the larger image size.

Read makebroden.sh first and trace how joingseg is used, comparing the existing 224, 227, and 384 dataset generation paths. Done means a 299 version is generated with its annotations and is usable by the referenced Inception_v3, NASNet, and PNASNet models.

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