Fix an issue where in a proper set of documentation, a field_info.annotation can be of type "type"

[mmangione]

This is a PR to fix the following issue:
#492

[mmangione]

@RobertoPrevato - Have you thought about appointing some maintainers? Some of these PRs are years old. Many of us want to help this library grow. I personally really like it and I use it extensively. I've deployed dozens of projects using it as a framework.

If you are running out of personal time, please consider letting the community help with the maintenance and upkeep.

[RobertoPrevato]

@mmangione good question, and thank you for your will to contribute. I indeed ran out of personal time for OSS in the last months, for a few personal reasons. I also dedicated a good deal of time to a private project implemented with BlackSheep, leaving me little time for the open source stuff. I'm happy to hear that my library has been useful for you, thanks for sharing - I mean it.