Peter M. Groen / oletools

Often you want to know size of a stream or re-set it to start, both of
which are not provided by ZipExtFile (result of ZipFile.open). Implement
both in own class.

…acro security (issue #221)

Will add excel test code and samples later, no need to have separate
folders for different file types.

This is in preparation of adding new function process_xlsx

…re process_file is called

This is based on the OpenXML specification (ISO 29500-1:2016 / ECMA-376)