* Update sub_types when calling update_forward_refs(), fix#404
* Update History
* Handle deeply nested ForwardRef types in sub_types using recursion
* Move update_field_forward_refs to utils.py
* fix ForwardRef collection bug, fix#439
* reformat codes
* minor document error
* add HISTORY.rst and simplified unit test
* restore the original example for ForwardRef
* support postponed annotations in python 3.7
* support for full ForwardRef
* tweak update_forward_refs
* better ForwardRef resolution
* remove debug, fix linting
* fix comments
* docs and history