llvm 2.5 release

I stubbed out some initial comments here in the llvm 2.5 release:

It would be nice to be more concrete about the various improvements we've made from around the 2.4 release timeframe. If you'd like to add or change anything in that section, please feel free to hack on llvm/docs/ReleaseNotes.html.

One advantage that clang has over llvm is that we're advertising Clang mainline, so we can describe the *current* state of Clang. :slight_smile:

Also, if anyone notices places in the clang web page that could be updated, now is a good time to do so - we usually get more web traffic immediately after releases.