Feature: preserveTimestamps

[jeffrson]

AFAICT: cpy uses graceful-fs, which in turn should use fs.copyFile to copy files. How fs.copyFile handles timestamps seems to be platform dependent. Now there's a new fs.cp in recent NodeJs versions that has a special option called preserveTimestamps, fs-extra has it too.

So I would like to propose to add this option in cpy as well - not only for files, but for directories too (cp -a).