Enforce max limit of characters

[sprain]

See specs 5.2 Maximum data range and QR code version

The maximum Swiss QR Code data content permitted is 997 characters (including the element separators).

[mikemeier]

@sprain Thanks for your library, we will soon start using it. Do you need help on open issues?

[sprain]

@mikemeier You are very welcome to contribute if you wish 🙌🏻