text: Title: Do an automatic stream flush before rendering a progress bar
  Body: 4.60.0 3.7.6 (default, Jan  8 2020, 20:23:39) [MSC v.1916 64 bit (AMD64)] win32
  Running Python in Spyder
  
  While tqdm is great for the negligible effort required to have a progress bar, I've found it necessary to add a `sys.stdout.flush()` call before usage to avoid possible interleaved output. This taints the code and reduces the ease of use. e.g. below, where although the `1` was printed before the bar was started, the output was interleaved.
  
  ```  
  1%|          | 14/2408 [00:00<00:17, 135.41it/s]1
  11%|█         | 263/2408 [00:02<00:17, 123.80it/s]
  ```
  
  An option to have tqdm automatically flush the output stream it's about to use would be a huge benefit. 