Look over error handling and include errors thrown in documentation of core

[louilinn]

https://circlesubi.github.io/circles-core/#coretokenfindtransitivetransfer

It would be helpful for projects using @circles/core package to know what error can be thrown by different functions such as
findTransitiveTransfer and updateTransitiveTransfer and transfer to better handle them. It should be clear when they occur and what they indicate.