Having two introduction sections in the navigation bar was awkward, here I've
left "introduction" as-is but changed "Introduction to 3.0" to "Release 3.0" and
"Release 3.0" to "Overview".
Modified Release Notes to be a brief overview of the 3.0 release
features, while moving the descriptive text to a new section that
outlines the major changes in 3.0 grouped along with the Porting
Guide and Subdivision Compatibility document.
