Requires that you have Git, NodeJS,
and Grunt (npm install -g grunt-cli) installed.
$ git clone https://github.com/openlayers/openlayers.github.io.git
$ cd openlayers.github.io
$ npm install
$ grunt
Currently this just builds API docs files for the master branch and puts
everything in build/doc. Next it will build API docs for multiple branches
as well as prose docs.