Can only load a file at a time on gcs

[pierrepesc]

Thanks for this package, it is extremely useful to be able to interact with google BQ and Storage.

However, it would be great if you could add this functionally : being able to load several files (e.g. *.png figures or *.csv files) in a single (blob.create) command.

Basically the same functionality than a drag drop of a bunch of files into the bucket on the gcs webpage. At the moment you need to create a blob for every single file you wish to upload into a bucket so when running a for loop over the list of files, it make the execution quite slow.

Cheers,