add compiler result field

ref: CompiledResult type at flow/compiler.js

Author: kazupon

packages/vue-template-compiler/README.md

@@ -22,6 +22,7 @@ Compiles a template string and returns compiled JavaScript code. The returned re
 
 ``` js
 {
+ ast: ?ASTElement, // parsed template elements to AST
  render: string, // main render function code
  staticRenderFns: Array<string>, // render code for static sub trees, if any
  errors: Array<string> // template syntax errors, if any