Add ids theme

Change-Id: I1b4a82a3ee14a7499293c639ad22221e4b60f4c3
diff --git a/R/revealjs_presentation.R b/R/revealjs_presentation.R
index 84614ae..881364f 100644
--- a/R/revealjs_presentation.R
+++ b/R/revealjs_presentation.R
@@ -337,6 +337,7 @@
 revealjs_themes <- function() {
   c(
     "default", # not used by reveal
+    "ids",
     "simple",
     "dark", # our alias for black
     "black",