Add 'latest release' info + changelog

[keunes]

This uses the jekyll-github-metadata gem and pulls the data from the GitHub API (it would need a periodic automated rebuild of the site in order to get the latest data; daily suggested). The content is then cached and does no 3rd party calls. Based on #163 Closes #99.

To do:

• try adding a light gray background below the expanded changelog
• remove the padding between the blue and the gray box, so that there is a single box with two colors instead of two boxes within each other

[ByteHamster]

• I find it a bit weird that the whole page moves when pressing that button.
• It is very prominent. More prominent than the download button. I would make it a lot less prominent.
• The line breaks seem to be missing