Help: Drop development topic notes to prepare release

Release versions do not have the development topic section of
the CMake Release Notes index page.
CMake 3.0.0-rc1 version update
Change version scheme to use only two components for feature levels

Historically CMake used three version components for the feature level.
We released new features while incrementing only the third version
component.  Since commit v2.8.2~105^2~4 (New version scheme to support
branchy workflow, 2010-04-23) we used the fourth version component for
bug-fix releases and the development date:

 <major>.<minor>.<patch>[.<tweak>][-rc<n>] = Release
 <major>.<minor>.<patch>.<date>[-<id>]     = Development

This solidified use of three components for the feature level, and was
necessary to continue releasing 2.x versions because:

* Some existing projects performed floating-point comparisons of
  ${CMAKE_MAJOR_VERSION}.${CMAKE_MINOR_VERSION} to 2.x numbers
  so ``x`` could never be higher than 9.

* Version 2.9.<date> was used briefly in post-2.8.0 development in
  CVS prior to the transition to Git, so using it in releases may
  have caused confusion.

Now that we are moving to 3.x versions, these two restrictions go away.
Therefore we now change to use only two components for the feature
level and use the scheme:

 <major>.<minor>.<patch>[-rc<n>] = Release
 <major>.<minor>.<date>[-<id>]   = Development
WIP: Begin post-3.0 development

TODO: Rebase on final release and fix date