tqdm v4.27.0 stable

• fix str.isnumeric #605
• fix WeakSet KeyError #548, #553, #596 -> #607
• stop tqdm_notebook description truncation #582 -> #599
• include unit_scale for rate #608
• add auto -> nowarning autonotebook
• add better postfix numeric formatting #621
• minor refactoring #609 -> #616
• update documentation
• add unit tests
• fix py26 CI