add escape special character

But your module was very useful, had the problem too.

For example case of problem is,

```javascript
var str = eval(hdoc)(function() {/*
  /* aaa */ //comment is terminated!!
*/);
```

then, I add a feature to escape special character to your module, for example

```javascript
var str = eval(hdoc)(function() {/*
  /* aaa *\/ //comment is continuing.
*/);
```

In short, `*` and `/` and `\` escape for comment, and `$` escape for embedding vals by putting `\`.