Use font-display: swap to ensure faster Web font display (#742)

See https://developer.mozilla.org/en-US/docs/Web/CSS/@font-face/font-display
for more information.

Author: Calinou

sass/_theme_font_local.sass

@@ -4,39 +4,44 @@
   src: url('../fonts/Lato/lato-regular.eot?#iefix') format('embedded-opentype'), url('../fonts/Lato/lato-regular.woff2') format('woff2'), url('../fonts/Lato/lato-regular.woff') format('woff'), url('../fonts/Lato/lato-regular.ttf') format('truetype')
   font-weight: 400
   font-style: normal
+  font-display: $font-display
 
 @font-face
   font-family: 'Lato'
   src: url('../fonts/Lato/lato-bold.eot')
   src: url('../fonts/Lato/lato-bold.eot?#iefix') format('embedded-opentype'), url('../fonts/Lato/lato-bold.woff2') format('woff2'), url('../fonts/Lato/lato-bold.woff') format('woff'), url('../fonts/Lato/lato-bold.ttf') format('truetype')
   font-weight: 700
   font-style: normal
-
+  font-display: $font-display
 
 @font-face
   font-family: 'Lato'
   src: url('../fonts/Lato/lato-bolditalic.eot')
   src: url('../fonts/Lato/lato-bolditalic.eot?#iefix') format('embedded-opentype'), url('../fonts/Lato/lato-bolditalic.woff2') format('woff2'), url('../fonts/Lato/lato-bolditalic.woff') format('woff'), url('../fonts/Lato/lato-bolditalic.ttf') format('truetype')
   font-weight: 700
   font-style: italic
+  font-display: $font-display
 
 @font-face
   font-family: 'Lato'
   src: url('../fonts/Lato/lato-italic.eot')
   src: url('../fonts/Lato/lato-italic.eot?#iefix') format('embedded-opentype'), url('../fonts/Lato/lato-italic.woff2') format('woff2'), url('../fonts/Lato/lato-italic.woff') format('woff'), url('../fonts/Lato/lato-italic.ttf') format('truetype')
   font-weight: 400
   font-style: italic
+  font-display: $font-display
 
 @font-face
   font-family: 'Roboto Slab'
   font-style: normal
   font-weight: 400
   src: url('../fonts/RobotoSlab/roboto-slab.eot')
   src: url('../fonts/RobotoSlab/roboto-slab-v7-regular.eot?#iefix') format('embedded-opentype'), url('../fonts/RobotoSlab/roboto-slab-v7-regular.woff2') format('woff2'), url('../fonts/RobotoSlab/roboto-slab-v7-regular.woff') format('woff'), url('../fonts/RobotoSlab/roboto-slab-v7-regular.ttf') format('truetype')
+  font-display: $font-display
 
 @font-face
   font-family: 'Roboto Slab'
   font-style: normal
   font-weight: 700
   src: url('../fonts/RobotoSlab/roboto-slab-v7-bold.eot')
   src: url('../fonts/RobotoSlab/roboto-slab-v7-bold.eot?#iefix') format('embedded-opentype'), url('../fonts/RobotoSlab/roboto-slab-v7-bold.woff2') format('woff2'), url('../fonts/RobotoSlab/roboto-slab-v7-bold.woff') format('woff'), url('../fonts/RobotoSlab/roboto-slab-v7-bold.ttf') format('truetype')
+  font-display: $font-display

sass/_theme_variables.sass

@@ -65,3 +65,5 @@ $base-font-family:                    "Lato", "proxima-nova", "Helvetica Neue",
 $custom-font-family:                  "Roboto Slab", "ff-tisa-web-pro", "Georgia", Arial, sans-serif
 $custom-font-family2:                 Georgia, serif
 $code-font-family:                    SFMono-Regular, Menlo, Monaco, Consolas, "Liberation Mono", "Courier New", Courier, monospace
+
+$font-display:                        swap