Update current weekly update issue & create next week's on Friday

Changes:

• Update 'nav' at the top to include "next" issue
• Add issue distribution by feature
• Improve details on how to use/where data comes from
• Add support for auto-adding threads; Add highlights thread
• Auto-add highlights to issue description on Fridays

Refactorings:

• Move bulk of markdown logic into separate Description class
• Move all gem imports to entrypoint
• Distill Generator to deal primarily with command line args & high-level actions