Add support for get() to keep downloaded file in memory via a BytesIO object as the "local_file"

[Michael Gillhofer]

Currently get() requires one to specify a path to a local file. This enforces the user to store the file to a path on the filesystem.
Add support for get() to keep downloaded File in memory via a BytesIO Object as the "local_file".

[Remi Rampin]

Duplicate of #94