Supply default option value only if the option is not specified

The "|| trick" is too brittle in this case -- it wouldn't work e.g. for
options with default value |true| and passed value |false|, enforcing
inconsistent default values handling.

src/emitter.js

@@ -1,7 +1,9 @@
 /* Emits the generated code for the AST. */
 PEG.compiler.emitter = function(ast, options) {
   options = options || {};
-  options.trackLineAndColumn = options.trackLineAndColumn || false;
+  if (options.trackLineAndColumn === undefined) {
+    options.trackLineAndColumn = false;
+  }
 
   /*
    * Codie 1.1.0