Update README and announcement for 3.0.2 release.

Fill in the release date (2014-10-06) and update the changes list.

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/branches/WX_3_0_BRANCH@77955 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775