New custom Jekyll plugin to bring Pure CSS Grids functionality into markdowns.
Replacing index.md HTML tags used for grids with new Jekyll grids plugin.
Replacing download.md HTML tags used for grids with new Jekyll grids plugin.
Splitting Media page entries into separate posts.
Integrating changes suggested by @elmindreda .

- Removing copyright notice from page footer.
- Temporarily disabling page footer.
- Fixed GLFW 3.0.2 changelog post.
- Small change to buttons appearance.
- Slight changes to the Documentation, Download, FAQ, Home and Media pages.
Bringing back Version history page previous look, so it can be easily searched.