support array in chalkboard reveal_options (#88)

fixes #62

Co-authored-by: christophe dervieux <christophe.dervieux@gmail.com>
diff --git a/tests/manual/test-plugin-chalkboard.Rmd b/tests/manual/test-plugin-chalkboard.Rmd
new file mode 100644
index 0000000..1f6c00b
--- /dev/null
+++ b/tests/manual/test-plugin-chalkboard.Rmd
@@ -0,0 +1,18 @@
+---
+title: "chalkboard plugin"
+output: 
+  revealjs::revealjs_presentation:
+    self_contained: false
+    reveal_plugins: ["chalkboard"]
+    reveal_options:
+      chalkboard:
+        theme: whiteboard
+        color: ['rgba(255, 0, 0, 0.3)', 'rgba(255, 0, 0, 0.3)']
+---
+
+# Configurations
+
+We are testing that color can be correctly change. 
+Pen is now red in both mode: Click on the left icons and write in Red. 
+
+Default is blue.