Implement a photo carousel

The layout of this is all CSS with scroll-snap. (Neat!) Also implement a
JavaScript scroll event listener that detects when photos scroll and
updates the caption and photo data.

Refactor a few parts of the photo_exif_table into partials so they can
be reused for the carousel items.

layouts/partials/photos/latitude.html

@@ -0,0 +1,4 @@
+{{ $lat := float .Lat }}
+{{ $latDir := cond (eq $lat 0) "" (cond (gt $lat 0) "N" "S") }}
+{{ $formattedLat := printf "%sº%s" (.Lat | lang.FormatNumber (cond (ne $lat 0) 3 0)) $latDir }}
+{{ return $formattedLat }}

layouts/partials/photos/longitude.html

@@ -0,0 +1,4 @@
+{{ $long := float .Long }}
+{{ $longDir := cond (eq $long 0) "" (cond (gt $long 0) "E" "W") }}
+{{ $formattedLong := printf "%sº%s" (.Long | lang.FormatNumber (cond (ne $long 0) 3 0)) $longDir }}
+{{ return $formattedLong }}

layouts/partials/photos/megapixels.html

@@ -0,0 +1,8 @@
+{{ $widthpx := .PixelXDimension }}
+{{ $heightpx := .PixelYDimension }}
+{{ $megapixels := 0 }}
+{{ if and (gt $widthpx 0) (gt $heightpx 0) }}
+  {{ $megapixels = div (mul $widthpx $heightpx) 1e6 }}
+{{ end }}
+{{ $formattedMegapixels := printf "%.0f MP" $megapixels }}
+{{ return $formattedMegapixels }}