Add hardLink option to grunt-contrib-copy

[xsellier]

I have a build process with grunt that copies a bunch of files (and does some other work). We truly need to preserve hard links.

The idea behind a hardLink option would be hard-link-if-you-can, and on platforms without that option it would do a copy, or copy when a hard link isn't possible (e.g., across devices).

[oitofelix]

I just published grunt-contrib-hardlink (initially forked from grunt-contrib-symlink) which solves the problem of a recursive hard-linking grunt task.