Fix form submission (#129)

* Fix check for radio and checkbox inputs

* Fix GET form submission

* Add example forms for testing

* Refactor query string building

lib/util/update-query-string.js

@@ -0,0 +1,10 @@
+module.exports = function(uri, key, value) {
+  var re = new RegExp("([?&])" + key + "=.*?(&|$)", "i")
+  var separator = uri.indexOf("?") !== -1 ? "&" : "?"
+  if (uri.match(re)) {
+    return uri.replace(re, "$1" + key + "=" + value + "$2")
+  }
+  else {
+    return uri + separator + key + "=" + value
+  }
+}