Squashed 'libs/impress.js/' content from commit 08f5690

git-subtree-dir: libs/impress.js
git-subtree-split: 08f569060ad57423ee6b01a4612146414d1c577d
Merge commit '402d06cca6053e53b8bd7a75e0ecc1498ba3e7f0' as 'libs/impress.js'