Switch to Jekyll for the site generation.

Todo: Fix `/downloads`, `/about` and `/changelog` pages.
Convert to Kramdown definition list
Converted downloads page
Converted About page
WIP: Convert Changelog
Note: trac links are not yet fixed
style.css: Add `padding-bottom` to container.

Fixes issue in some news posts.
Switch to Grunt for building everything.
Implement filename-based cache busting for css and js files.
Fix changelog.md trac links.
Separate layouts.
changelog.md: Fix nested lists.
Be consistent with the header markdown.
Add html validation test.
Fix validation errors.
Add JSHint check.
Test everything with Travis.
Move version defines in the Grunt task.

We already have them there so there's no need to duplicate stuff.
Support only Node.js 0.10.x.

If/when 0.11 is released we'll test against it again.
Switch to the new dependency badge.
Move files into source.