Uniform fixed-width fonts.

Merged the fonts declaration of the pre and code,kbd,samp blocks to
use the same fallbacks.

Author: JGiola

README.md

@@ -152,6 +152,7 @@ code, kbd, pre, samp {
     /* Windows 6+ */ Consolas,
     /* Android 4+ */ Roboto Mono,
     /* Ubuntu 10.10+ */ Ubuntu Monospace,
+    /* KDE Plasma 5+ */ Noto Mono,
     /* KDE Plasma 4+ */ Oxygen Mono,
     /* Linux/OpenOffice fallback */ Liberation Mono,
     /* fallback */ monospace;

sanitize.css

@@ -124,6 +124,7 @@ pre {
     /* Android 4+ */ Roboto Mono,
     /* Ubuntu 10.10+ */ Ubuntu Monospace,
     /* KDE Plasma 5+ */ Noto Mono,
+    /* KDE Plasma 4+ */ Oxygen Mono,
     /* Linux/OpenOffice fallback */ Liberation Mono,
     /* fallback */ monospace; /* 1 */
 
@@ -173,6 +174,7 @@ samp {
     /* Windows 6+ */ Consolas,
     /* Android 4+ */ Roboto Mono,
     /* Ubuntu 10.10+ */ Ubuntu Monospace,
+    /* KDE Plasma 5+ */ Noto Mono,
     /* KDE Plasma 4+ */ Oxygen Mono,
     /* Linux/OpenOffice fallback */ Liberation Mono,
     /* fallback */ monospace; /* 1 */