Added grunt task to copy docs from the jquery/foundation repo.

This is a standalone task that isn't run during deploy. There are two reasons for this:

1) Contributors won't be able to run this task since it accesses a private repo.

2) The docs that get copied become pages, which are managed via git. We wouldn't want a deployment to create local changes.

The idea is that board members would be able to run this task after a document changes and commit the results. I implemented this with a token in a config file, but we could also prompt the user for their GitHub username and password. This just seemed easier.