Wrap PixhawkInstruction values in `float()`

`PixhawkInstruction` values must be floats. Python is weird, so computed values should be passed through the `float()` function before being passed to `PixhawkInstruction()`. i.e.

```python
PixhawkInstruction(
    forward=float(0.5),
    vertical=float(-0.25),
    author=PixhawkInstruction.MANUAL_CONTROL
)
```

Write instructions to that effect.