bump version, merge branch 'slack'

bump version, merge pull request tqdm#1311 from tqdm/devel

fix stderr/stdout missing `flush()`

- closes tqdm#1248
- re-fixes tqdm#1177

bump version, merge pull request tqdm#1302 from tqdm/devel

bump version, merge pull request tqdm#1246 from tqdm/devel

bump version, merge pull request tqdm#1229 from tqdm/devel

bump version, merge pull request tqdm#1222 from tqdm/devel

bump version, merge pull request tqdm#1209 from tqdm/devel

Merge pull request tqdm#1180 from tqdm/devel

bump version, merge pull request tqdm#1180 from tqdm/devel

bump version, merge pull request tqdm#1175 from tqdm/devel