Last modified date on resource?

[dafeder]

It seems last_modified was removed from both data package and data resource with very little discussion early in the project and has not come up since. It makes sense that this not be a required field but it's surprising to me that there is no standardized way to express either a version or timestamp for resource files.

I can see that last_modified is confusing at the package level. Does it mean the last time the package-level metadata was modified, the last time any metadata at any level was modified, or the last time any resource listed in the package was modified? On the other hand, it seems fairly unambiguous that last_modified on a resource would mean the time of the last modification to the resource file. Would it make sense to propose this as a recipe at least?