almagamate includes/ and vendor/ dirs

```bash
├── includes
│   └── OAuth.php
└── vendor
    ├── bootstrap
    └── log4php

29 directories, 216 files
```

There is no need for an `includes/` and a `vendor/` dir given that `includes/` only has one item. Move `OAuth.php` (which is needed for building oauth1 consumer's) to `vendor/` and delete `includes/` dir.