Copy fileobj into member buffer when creating Package

[ngparas]

Because the fileobj isn't copied into a buffer local to the Package instance we require resets outside of the class e.g. https://github.com/UptakeOpenSource/cran-server/blob/master/cranserver/server.py#L88

The constructor should copy the fileobj into a new BytesIO

[bburns632]

Thank you for your interest. However, this project will be archived shortly. More details in #77 .