FEATURE: add a setting to allow url schemes other than http(s)

test/javascripts/mdtest/mdtest.js.es6.erb

@@ -37,9 +37,9 @@ function sanitizer(result, whiteLister) {
   return result;
 }
 
-function md(input, expected, text) {
+function md(input, expected, text, settings) {
 
-  const opts = buildOptions({ siteSettings: {} });
+  const opts = buildOptions({ siteSettings: settings||{} });
   opts.traditionalMarkdownLinebreaks = true;
   opts.sanitizer = sanitizer;
 
@@ -77,3 +77,11 @@ test("first", function(){
 %>
 
 <%= mdtest_suite %>
+
+test("whitelisted url scheme", function() {
+  md("[Steam URL Scheme](steam://store/452530)", '<p><a href="steam://store/452530">Steam URL Scheme</a></p>', 'whitelists the steam url', {allowed_href_schemes: "macappstore|steam"});
+});
+
+test("forbidden url scheme", function() {
+  md("[Steam URL Scheme](steam://store/452530)", '<p><a>Steam URL Scheme</a></p>', 'removes the href', {allowed_href_schemes: "macappstore|itunes"});
+});