Use escape instead of noescape in _opts

Make the escaping option similar to `prettify` in `_opts` by making it
positive. The `_opts` option `prettify` is exposed in CLI as
--no-prettify, similarly to `escape` exposed as --no-escape.

Refactor.

Corollary of hacksalot#219

src/renderers/handlebars-generator.js

@@ -38,7 +38,7 @@ module.exports = {
       template = HANDLEBARS.compile(tpl, {
         strict: false,
         assumeObjects: false,
-        noEscape: data.opts.noescape
+        noEscape: !data.opts.escape
       }
       );
       return template(data);

src/verbs/build.js

@@ -194,7 +194,7 @@ var _prep = function( src, dst, opts ) {
   _opts.theme = (opts.theme && opts.theme.toLowerCase().trim()) || 'modern';
   _opts.prettify = opts.prettify === true;
   _opts.private = opts.private === true;
-  _opts.noescape = opts.escape === false;
+  _opts.escape = opts.escape === true;
   _opts.css = opts.css;
   _opts.pdf = opts.pdf;
   _opts.wrap = opts.wrap || 60;