Redirect the old Packaging Guide

[rkratky]

Redirects need to be put in place from the old Packaging Guide:

1. Page-level redirects from v1.0: https://canonical-ubuntu-packaging-guide.readthedocs-hosted.com/en/1.0/
2. Site-level redirects from v2.0-preview (latest): https://canonical-ubuntu-packaging-guide.readthedocs-hosted.com/en/latest/

In addition, the following should be (site-level_ redirected to this docs set:

• https://ubuntu-packaging-guide.readthedocs.io/en/latest/ (currently 404s)
• https://ubuntu-packaging-guide.readthedocs.io/_/downloads/en/stable/pdf/
• https://ubuntu-packaging-guide.readthedocs.io/en/latest/ubuntu-packaging-guide/

Finally, https://wiki.ubuntu.com/Spec/UbuntuPackagingGuide should link to this docs set.

[rkratky]

Also: #134