JS-less photo grids with `display: flex`

Created Sep 30, 2015 by Pascal Hertleif and published in Pascal's Scribbles. Labeled as incomplete and css.

pascalhertleif.de/fotos has (inline, template-generated) CSS setting CSS3 flex properties to align photos of different sizes (but with max-width/max-height) without JS.

TODO: Describe this magic here.