Some b2d methods get incorrectly sanitized

```
Modifying invalid string "joint.get_damping_ratio" to "joint_get_damping_ratio"
Modifying invalid string "joint.get_world" to "joint_get_world"
Modifying invalid string "body.get_next" to "body_get_next"
```

These methods should be:
- `b2d.joint.get_damping_ratio`
- `b2d.joint.get_world`
- `b2d.body.get_next`