Add support for the space character for the show-invisibles plugin

This patch adds a bit of position magic, so that the invisibles
are displayed on top of the original character. This allows for
the inclusion of the space character.

plugins/show-invisibles/prism-show-invisibles.css

@@ -1,7 +1,16 @@
+.token.tab:not(:empty),
+.token.cr,
+.token.lf,
+.token.space {
+	position: relative;
+}
+
 .token.tab:not(:empty):before,
 .token.cr:before,
-.token.lf:before {
+.token.lf:before,
+.token.space:before {
 	color: hsl(24, 20%, 85%);
+	position: absolute;
 }
 
 .token.tab:not(:empty):before {
@@ -18,3 +27,7 @@
 .token.lf:before {
     content: '\240A';
 }
+
+.token.space:before {
+	content: '\00B7';
+}

plugins/show-invisibles/prism-show-invisibles.js

@@ -14,5 +14,6 @@ Prism.hooks.add('before-highlight', function(env) {
 	tokens.crlf = /\r\n/g;
 	tokens.lf = /\n/g;
 	tokens.cr = /\r/g;
+	tokens.space = / /g;
 });
 })();