Many numerical values are stored as strings

[oobayly]

Properties that contain number, such as GoCardless.Resources.TaxRate.Percentage or GoCardless.Resources.PayoutItem.Amount are presented as strings. This makes very little sense as they're numbers, and raises a few questions:

1. Can they be null or an empty string, or are they guaranteed to be parsed safely?
2. What locale do we parse them in?
3. Are we guaranteed that the decimal separator is always .,
4. Are we guaranteed that there will never be a decimal separator.

It seems a bizarre decision to make, especially as other properties are integers, eg. GoCardless.Resources.Payout.Amount, etc.