new mkrelease script for OS X

This commit does a few things:
1. includes a new mkrelease script for OS X devs to bundle releases with
2. removes the old Perl scripts that sort of accomplished the same task
3. includes a README documenting how to use the new script

The old scripts were brittle and inefficient.

The new script is written in Ruby because it is what I'm familiar with and because OS X has shipped with Ruby since version 10.5.0.