Consider merging GNU and POSIX templates and use getopt/getopts based on availability

Using this pattern, we can detect whether GNU getopt is available and use it:

```
getopt -T > /dev/null
if [ $? -eq 4 ]; then
    # GNU enhanced getopt is available
    set -- `getopt --long help,output:,version --options ho:v -- "$@"`
else
    # Original getopt is available
    set -- `getopt ho:v "$@"`
fi
```