Merge pull request #548 from Gubolin/issue_361

allow percent symbols in custom block texts (fix #361), thanks again @Gubolin, both for the fix and for your patience!

byob.js

@@ -227,7 +227,7 @@ CustomBlockDefinition.prototype.blockSpec = function () {
         parts = this.parseSpec(this.spec),
         spec;
     parts.forEach(function (part) {
-        if (part[0] === '%') {
+        if (part[0] === '%' && part.length > 1) {
             spec = myself.typeOf(part.slice(1));
         } else {
             spec = part;
@@ -311,7 +311,7 @@ CustomBlockDefinition.prototype.inputNames = function () {
     var vNames = [],
         parts = this.parseSpec(this.spec);
     parts.forEach(function (part) {
-        if (part[0] === '%') {
+        if (part[0] === '%' && part.length > 1) {
             vNames.push(part.slice(1));
         }
     });