Lets-do-dns

Fixes a bug with the `PATH` variable being sent to the `LETS_DO_POSTCMD` program upon execution.

This version fixes an issue where the `CERTBOT_HOSTNAME` variable was not being passed to the `LETS_DO_POSTCMD` program when it was being run.

This version includes a Dockerfile for easy installation within a containerized environment, building off of the EFF's pre-existing certbot/certbot Docker image.

It also includes a critical fix involving the DNS resolution check during the authentication stage that was not being performed correctly as well as a fix in the setuptools setup.py file that incorrectly reported the GitHub download URI.

First public release of the lets-do-dns program!

This release provides a fully functional authentication and cleanup hook program for the EFF's certbot program that handles using DigitalOcean's REST API for modifying authentication DNS records required by certbot to validate your ownership of a hostname that it's creating a certificate for. It also supports calling another program upon completion that can be used to trigger restarting server processes.