added from_generator method to IterableDataset class.
_The documentation is not available anymore as the PR was closed or merged._ I added a test and moved the `streaming` param from `read` to `__init_`. Then, I also decided to update the `read` method of the rest of the packaged modules to account for this param. 

@hamid-vakilzadeh Are you OK with these changes?  @mariosasko these all look great! Thanks for the updates.
Hello, 

This resolves issues #4988.

I added a method `from_generator` to class `IterableDataset`.

I modified the `read` method of input stream generator to also return Iterable_dataset.
