Added express middleware support

 * Added express middleware support.
 * Normalized the default global variable exported from the package for consistency. Some docs read "Foo" some read "App" and the code defined it as "foo". 

Default implementation should look like:

```
var express = require('express');
var glue = require('gluejs').middleware;

var app = express();

app.use(express.logger('dev'));

app.use('/js/app.js', glue({
  include: './public/js'
}));
app.use(express.static(__dirname + '/public'));

app.listen(3000);
```

Notice that `include` option is the only required parameter. The `basepath` will default to the `include` path and the `main` file will default to `index.js` in the `include` path. All other options can be defined in the hash as well. 

Let me know if you have any questions/comments/improvements.