Custom rendering: Teletype support

app/src/main/java/eu/faircode/email/HtmlHelper.java

@@ -45,6 +45,7 @@ import android.text.style.StrikethroughSpan;
 import android.text.style.StyleSpan;
 import android.text.style.SubscriptSpan;
 import android.text.style.SuperscriptSpan;
+import android.text.style.TypefaceSpan;
 import android.text.style.URLSpan;
 import android.text.style.UnderlineSpan;
 import android.util.Base64;
@@ -2002,6 +2003,9 @@ public class HtmlHelper {
                             case "s":
                                 ssb.setSpan(new StrikethroughSpan(), start, ssb.length(), Spanned.SPAN_EXCLUSIVE_EXCLUSIVE);
                                 break;
+                            case "tt":
+                                ssb.setSpan(new TypefaceSpan("monospace"), start, ssb.length(), Spanned.SPAN_EXCLUSIVE_EXCLUSIVE);
+                                break;
                             case "u":
                                 ssb.setSpan(new UnderlineSpan(), start, ssb.length(), Spanned.SPAN_EXCLUSIVE_EXCLUSIVE);
                                 break;