pre-commit is run just before a commit is made. The script checks
all added/modified php files for their headers. Currently it checks
for the existence of the modification date (current date) copyright
year (current year) and author (name/email from the git config). If
one of the checks fails the commit is aborted.
The pre-commit hook requires python 3. Install the hook by running
create_hook_symlinks.sh which will create a symlink in .git/hooks