Cleanup/finition tasks for v1.0

[niconoe]

Code

• Rename sample test files for more clarity/consistency (drop the helper CONSTANTS, they add complexity for nothing)
• Fix various issues reported by Flake8
• Clarify folder/directory terminology in doc, code and comments
• Search and fix TODO's across the code

Documentation

• document different kinds of supported archives (doc homepage?)
• document support for Py2/Py3
• document: how to detect what kind of archive is in use
• adds a glossary page/section for terms such as Metafile, Simple archive, Metadata, row, ...