Changes to _includes/head.html

[PeterWhittaker]

• Remove gmpg
• Use none of the xmlns, utf-8 headers (cf colophon, default.html, etc.)
• Use the x-ua-compatible, ie=edge - this forces IE to use most recent engine available: ''
• Retain hyde.css (duh)
• Use the P icon, since it looks like Peter. Later, get a better one.
• Keep the Google Fonts (Abril, PT), keep the Hyde.css fonts bits as they are.
• Create a colophon asking people to comment about rendering problems, which I will fix as needed: I'm going to
  skip all UTF-8 specifications.
• Use atom specification from "Peter", not RSS from "Hyde"