Allow negative positional parameters
Allow negative positional parameters

Using negative values errors with:

```
$ bpftrace -e 'i:ms:100 { printf("%llx\n", $1); }' -- -5
$1 used numerically but given "-5". Try using str($1).
```

This is due to `-` not being a digit. By switching to `stoll` we can
allow a much wider range of values with support for different bases.

iovisor/bpftrace,iovisor/bpftrace,iovisor/bpftrace,iovisor/bpftrace