Scripting language plugins for the Incubator

This includes a Perl and a Python destination. Both work similarly: they call an `init` and a `deinit` function at appropriate times, without arguments. They can return a value, which will indicate success or failure. Both use value-pairs to set up a hash map or dictionary to pass to the `queue` function, which can also return a bool-ish value.

The Python destination also supports an `import()` statement, which can be used to pre-load python modules before loading the script itself.

Both modules use LogThreadedDestination. There may be issues, such as when trying to use two perl or python destinations, those problems - if any - will be corrected in a followup PR.