Fix inclusion of block using a simple function

lib/page/html.js

@@ -110,7 +110,7 @@ HTMLPipeline.prototype.transformCodeBlocks = function() {
 
         return Promise(this.opts.onCodeBlock(source, lang))
         .then(function(blk) {
-            if (blk.html !== true) {
+            if (blk.html === false) {
                 $code.text(blk.body);
             } else {
                 $code.html(blk.body);

lib/plugins/plugin.js

@@ -282,7 +282,7 @@ BookPlugin.prototype.getBlocks = function() {
     var that = this;
 
     return _.mapValues(this.content.blocks || {}, function(block, blockName) {
-        block = _.isFunction(block)? { exec: block } : block;
+        block = _.isFunction(block)? { process: block } : block;
 
         var fn = block.exec;
         block.exec = function() {

lib/template/blocks.js

@@ -7,5 +7,10 @@ module.exports = {
 
     // Highlight a code block
     // This block can be replaced by plugins
-    code: _.identity
+    code: function(blk) {
+        return {
+            html: false,
+            body: blk.body
+        };
+    }
 };

lib/template/index.js

@@ -146,12 +146,15 @@ TemplateEngine.prototype.addBlock = function(name, block) {
     block = _.defaults(block || {}, {
         shortcuts: [],
         end: 'end'+name,
-        process: _.identity,
         blocks: []
     });
 
     extName = blockExtName(name);
 
+    if (!block.process) {
+        throw new Error('Invalid block "' + name + '", it should have a "process" method');
+    }
+
     if (this.hasBlock(name) && !defaultBlocks[name]) {
         this.log.warn.ln('conflict in blocks, "'+name+'" is already defined');
     }