Set all hashbangs to /usr/bin/env perl

[tseemann]

Currently all the perl scripts start with

#!/usr/bin/perl

The preferred behaviour is

#!/usr/bin/env perl

This will ensure that the first perl the $PATH will be used. This has become much more important with modern packaging system like conda and brew which do not use the system installed perl.

This updates PR #25

[tseemann]

Thank you @weizhongli !