* update ci-testing.yml

* update greetings.yml

* bring back os matrix

* update ci-testing.yml

* update greetings.yml

* bring back os matrix

* Enable direct `--weights URL` definition

@kalenmike this PR will enable direct --weights URL definition. Example use case:
```
python train.py --weights https://storage.googleapis.com/bucket/dir/model.pt
```

* cleanup

* bug fixes

* weights = attempt_download(weights)

* Update experimental.py

* Update hubconf.py

* return bug fix

* comment mirror

* min_bytes

add Open in Kaggle badge

* Update datasets.py

* comment

Co-authored-by: Glenn Jocher <glenn.jocher@ultralytics.com>

* COCO evolution fix

* cleanup

* update print

* print fix

Returns `True` if file is part of pip package. Useful for contextual behavior modification.

```python
def is_pip():
    # Is file in a pip package?
    return 'site-packages' in Path(__file__).absolute().parts
```

This reverts commit 21a9607.

* Update README.md

* Changing FLOPS to FLOPs.

Co-authored-by: BuildTools <unconfigured@null.spigotmc.org>

* Parse URL authentication

* urllib.parse.unquote()

* improved error handling

* improved error handling

* remove %3F

* update check_file()

* Suppress jit trace warning + graph once

Suppress harmless jit trace warning on TensorBoard add_graph call. Also fix multiple add_graph() calls bug, now only on batch 0.

* Update train.py

Per VOC empirical results #3380 (comment) by @developer0hye

* Add `timeout()` class

* rearrange order

remove datatype conversion process that can be skipped

* Add check_git_status() 5 second timeout

This should prevent the SSH Git bug that we were discussing @kalenmike

* cleanup

* replace timeout with check_output built-in timeout

Improve robustness of `check_requirements()` function to offline environments (do not attempt pip installs when offline).

* Add output names & dynamic axes for onnx export

Add output_names and dynamic_axes names for all outputs in torch.onnx.export. The first four outputs of the model will have names output0, output1, output2, output3

* use first output only + cleanup

Co-authored-by: Samridha Shrestha <samridha.shrestha@g42.ai>
Co-authored-by: Glenn Jocher <glenn.jocher@ultralytics.com>

* fixed inference bug ,while use half precision

* replace --use-half with --half

* replace space and PEP8 in detect.py

* PEP8 detect.py

* update --half help comment

* Update test.py

* revert space

Co-authored-by: Glenn Jocher <glenn.jocher@ultralytics.com>

* Update stale.yml

* cleanup

* Update stale.yml

* reformat

* call model.eval() when opt.train is False

call model.eval() when opt.train is False

* single-line if statement

* cleanup

Co-authored-by: Glenn Jocher <glenn.jocher@ultralytics.com>

Fix for 3rd party or contrib versions of installed OpenCV as in #3494.

* early assert for cpu and half option

early assert for cpu and half option

* Modified comment

Modified comment

* Update README.md

Minor modifications

* 850 width

revert greeting change as PRs will now merge to master.