A mostly inconsequential name change

It’s been brought to my attention that a game called Spectrum has been released, and in the interest of not causing any confusion, I’ve renamed my open-source game system to Spectra. It’s been a dormant project for years, but I think I want to revive it, and this would head off any potential miscommunication.

The updated document is still incomplete and looking for contributors; you can access the latest edition here (https://drive.google.com/open?id=1y2WLB14sFRVsndtI0pu7VRCQdtVHi9N8)