Add bash script for updating copyright headers

This script is largely inspired from a Request from Curtis Rueden and should
be called with a positional argument equal to the current year, e.g.
$ bash tools/update_copyright 2015
Split pattern
Add logic to update single year copyrights
Attempt to fix sed issue
Add check for copyright year arguments
Merge pull request #1462 from sbesson/copyright_tools

Add bash script for updating copyright headers