Update documentation for 'file' module to include 'diff_peek'.
Update documentation for 'file' module to include 'diff_peek'.

The 'diff_peek' option isn't documented at all, and provides a
rudimentary check that the content isn't binary. Documentation is
added to explain the option.

The 'validate' option has a declaration, but isn't implemented.
Therefore it may as well be removed from the module.

thaim/ansible,thaim/ansible