* Rename libexec_dir to apache_libexec_dir

This works around an issue when using this cookbook with the docker cookbook at
the same time. They both have a function called ``libexec_dir`` and docker seems
to override this cookbook. To work around this, renaming our function to
``apache_libexec_dir`` seems to work.

This resolves #677.

* Disable MD024 because we follow Keep A Changelog syntax which conflicts