Global transformers package imports, render local changes to the transformer src code useless for example scripts 
# 🚀 Feature request

In the summarization.py example file, it imports the global transformers package not the src/transformers package making local development challenging.  I'd like to make changes to the trainer.py file within src/transformers/trainer.py and have those changes reflected when I run the examples/pytorch/summarization/run_summarization.py script.  However due to the current package structure in the repository as is - the transformers folder isn't a package on its own and thus setting up a system of relative imports to access this folder from the examples directory is hoping through a lot of loops to avoid errors such as `attempted relative import with no known parent package`.  The repo structure also makes it hard to move the example file into the transformers package since none of the higher level folders are packages themselves causing the same issue.  


## Motivation

Not having this entire repo structured as packages makes it really challenging and not straight forward for someone who wants to experiment with making changes to the models and training exposed through this library.  The provided scripts to run various tasks and train are helpful however since they use global imports they hardly work well with the rest of the repo and might as well be stand alone repositories by themselves.  

## Your contribution

@patil-suraj  has mentioned he would be a point of contact for the summarization examples repo directly.  Would first ask if he has suggestions into how this can be best addressed  (other than asking everyone facing this to restructure the repo into packages etc themselves), otherwise I am looking into getting that restructure done just since its blocking in terms of making any updates and seeing that reflected when running these training scripts.

Support here would make a huge difference to the accessibility / extensibility of these provided example scripts and notebooks.

Hello! Maybe I misunderstood your issue, but if you clone the repository and install it as an editable package, you should be able to run the `run_summarization` script with the changes you have made.

```
git clone https://github.com/huggingface/transformers
cd transformers

pip install -e .
```<|||||>This issue has been automatically marked as stale because it has not had recent activity. If you think this still needs to be addressed please comment on this thread.

Please note that issues that do not follow the [contributing guidelines](https://github.com/huggingface/transformers/blob/master/CONTRIBUTING.md) are likely to be ignored.