feat: refactor script and add perl as an interpreter

[wolfv]

This adds perl as an interpreter, and I verified that the following "works":

package:
  name: test-perl-exec
  version: "0.1.0"

build:
  script:
    interpreter: perl
    content: |
      use strict;
      use warnings;
      use Config;

      print "Hello World!\n";
      print "Perl prefix: $Config{prefix}\n";

requirements:
  build:
    - perl

We can add support for R, nodejs, and a number of other languages in the same way.

cc @danielnachun

[wolfv]

This should also help with writing tests for perl (#790)