Verification for missing files

[IdoGuzi]

Hey @mhiyer I tried using the script on the COCO2017 validation set and there was 48 missing .xml file. so I "wrote" (mostly copy pasted some of your code) an verification script ("verify.py") to create the .xml for the missing images with no object data.

i only added 2 lines to the readme about the usage. it will be cool if you check it out, or add this feature how ever you like.

[mhiyer]

Hi @IdoGuzi, thanks so much for taking the time to improve this code. I'll have a look