Mixins: Add Golden Ratio function

Requested in #1222
Reduced heading bottom margins to 0.25em (#1222). Also pe.resize is no longer called for old IE in the pe-ap.js dance function since not needed (#974).
Fixed dance conditional for pe.resize.
Updated readme and top level pages with v3.1.0-b2 and v3.0.5 release information.
Cleanup: Combine IE7 and 8 JS SCSS
Merged sheets, but no real optimization done at this point.
Tagged follow up issue with thte tabbed interface and opacity mixins