nflplays

Hi there,

I've added fields for `DRIVE_ID` and `REL_PLAY_ID`, and noted the errors I found in the dataset along the way.

(There are more than a few git repos with this exact same data, while yours is the first one that appears to be trying to improve it rather than just use it. It would be great if the original post by Brian Burke referenced this repo...This dataset needs more than a little work, sadly.)

-Jay