Tqdm

- Thread safety! (285 -> 291 -> 329, 407, 417)
- Ease redirection of `sys.stdout`/`stderr` (422)
- Minor internal stream bugfix (439)
- `AttributeError` fixes (323, 324, 418)

Related to:

- Misc bugs (334)
- `concurrent.futures` (97)
- Multi-`tqdm` (143)
- `flush()` and `refresh()` (331)
- Newline on `refresh()` (361)
- Nested trees (384)
- Manually positioned nested bars clearing (385)

- initialise `n` even when disabled (438)
- better unicode detection (437)
- `__repr__()` bugfix (441)

- easier redirect of `stdout` (426 -> 431)
- `cls.external_write_mode() contextmanager`
- `refresh=True` for `set_description`/`update`(`_str`) (317 -> 377)

- more formatting control (347 -> 362)
- `set_postfix_str()`, `set_description_str()`
- move `": "` to `bar_format`
- complements 266, 270
- better CLI support (e.g. hyphenated paths) (421 423 -> 424)
- more unit tests (411)
- upgrade to pypy2/3-5.8.0
- add py37-dev
- doc updates

- minor fixes (395)
- minor documentation updates (400, 401, 412)
- better `pandas` support (351 -> 409)
- Jupyter notebook fix (352, 369 -> 373, 405)
- optimise `setcheckinterval`/`setswitchinterval` (376)
- add `unit_scale` (273, 295 -> 378)

- add `unit_divisor` 354 -> 356
- update examples