Support for encrypting numbers

Hey folks,

I recently started using this for a hobby project and noticed that it is possible to encrypt Strings only.

```
Error: encryption enabled for field amount of unsupported type Float: only String fields can be encrypted.
```

Is there some inherent plugin/cryptography limitation to encrypting numbers, or was this just never a priority to implement?

If someone could give me a couple of hints around this I'd love to take a stab at implementing support for it.