Sopport for gfs.json

[liubgithub]

Hi,Mourner, thanks for your great work, I have made a maptalks layer heavily based on your project, here is it: https://github.com/liubgithub/maptalks.wind .
You have used the wind texture as a look up table to get wind speed。My question is how can I sopport the gfs.json.
The gfs.json's stucture is like the screenshot: