Add link buttons to readme and automate gh-pages generation

In order to use the gh-pages generator without the need to tweak the generated result afterwards, this change makes it so the link buttons for release download, examples and api docs are included directly in the readme, which feeds the content of the generated gh-pages entry page.

The `build/publish.sh` script adds the distribution contents to the gh-pages branch. So there is no need any more to manually edit gh-pages, because website generation is a 2-step process:

1. Run the page-build generator on github (only required when README.md changes)
1. Run `build/publish.sh`