Clarify documentation for the wheel specification

[mihaigiurgeanu]

Issue Description

I find the documentation extremely hard to read and time consuming. Very badly written.

Examples:

• In Binary Distribution Format section, Details chapter is before File Format chapter, making forward references to distribution-1.0.dist-info/WHEEL, distribution-1.0.data/. Some things are not defined at all, like what is purelib, what is patlib?

• In Overview of the Python Packaging, there is so little about the actual source and binary packaging and so much about Packaging Python applications. Packaging Python applications is just a discussion and its place should be in a Anexa or something, and not wasting reader's time with useless information.

How should documentation be improved

1. No forward references
2. Be concise and precise.
3. Move discussions to separate sections. There is a discussion section, but a lot of useless text for the reader is into the overview section as well.

Code of Conduct

• I am aware that participants in this repository must follow the PSF Code of Conduct.

[ncoghlan]

The packaging overview is the way it is because the vast majority of Python developers will never need to ship a library of their own, they'll be shipping applications. The discussion of application packaging in the overview is longer than that for library packaging because the library section mostly consists of references off to dedicated sub pages on more specific topics (either tutorials, guides, or actual specifications). For folks shipping applications, we actually want them to hit the overview and bounce (since many of the potential considerations in shipping applications aren't Python specific)

The quirky structure of the binary distribution format documentation is inherited from the approved version of the original specification, which was sufficient to allow the proposal to be implemented by Python installation tool authors, but isn't particularly clear to readers that aren't already familiar with the post-installation filesystem layout specification that it was based on (for example, purelib vs pathlib is an installation time concept, now defined in https://docs.python.org/3/library/sysconfig.html#installation-paths).

Accordingly, I'm narrowing the scope of this issue purely to cover editorial changes to the wheel specification documentation that don't change the definition of that format, but do change how it is described to avoid assuming that the only target audience is folks that are already know how packages are installed onto a local filesystem.