Update buildbot.net web site

Hi,

I think that the main buildbot.net web page is a bit dated,
and doesn't represent the best about buildbot.

I have some suggestions for improving the web page, and was
wondering what people think about these ideas:

(1) Delete pretty much all the text starting with *Buildbot Basics*.
I haven't found that text useful for understanding Buildbot or what it can do.
The diagram isn't helpful, and looks pretty dated, especially with DARCS. :)

(2) Have a widget on the web page, which has links to the latest blog posts.
The latest blog posts have been really interesting, such as Kubernetes,
writing UI extensions with Flask, etc.
For example, look at https://jenkins.io

(3) Have a prominent *Download* button that is one of the first things people see when

(4) Have a link to http://nine.buildbot.net so people can see the working buildbot in action.

(5) Maybe have a widget with latest #buildbot Tweets.