Fix cutoff char bug && add theme feature

Cutoff character bug
------------------------

With a simple jade template, `layout.jade`:

```
doctype 5
html
  body
```

And a simple render:

```
exports.index = (req, res) ->
  res.render 'layout'
```

The html that results after mixing in the EDT markup cuts off the closing bracket of the starting body tag, looking in part like this:

```
<!DOCTYPE html><html><body<style type="text/css">/* SHOW/HIDE buttons */
#EDT-show {
...
```

Theme feature
-----------------

Added ability to pass in css as a theme to override the default css.  Used like:

```
settings = { theme: path.join(__dirname, 'static, 'css', 'express-debug.css') };
app.use(require('express-debug')(settings));        
```

Sorry these came together in one pull request.  I should have feature branched.