Generate source maps

Allow the precompiler to generate source maps when the srcFile parameter is passed.

This refactors large chunks of the code generation pipeline, allowing metadata to be associated with code chunks as well as breaking out much of the code generation logic into a separate helper.

spec/expected/empty.amd.js

@@ -1,6 +1,6 @@
 define(['handlebars.runtime'], function(Handlebars) {
   Handlebars = Handlebars["default"];  var template = Handlebars.template, templates = Handlebars.templates = Handlebars.templates || {};
 return templates['empty'] = template({"compiler":[6,">= 2.0.0-beta.1"],"main":function(depth0,helpers,partials,data) {
-  return "";
+    return "";
 },"useData":true});
 });