std.zip: Update and correct main documentation

[ghost]

I replaced the link below "zip archive" to the wikipedia entry, because the old link points to the zip/unzip utility webpage which contains information about this utility but not about zip archieves in general.

Further: From the 6 listed bugs, the first four are no bugs, but just limitations of the current implementation. Bug 592 is "won't fix", refering to D1; Bug 2137 is allready fixed. Therefore I removed the two real bugs and replaced the headline by "Limitations".

[dlang-bot]

Thanks for your pull request and interest in making D better, @crocopaw! We are looking forward to reviewing it, and you should be hearing from a maintainer soon.
Please verify that your PR follows this checklist:

• My PR is fully covered with tests (you can see the coverage diff by visiting the details link of the codecov check)
• My PR is as minimal as possible (smaller, focused PRs are easier to review than big ones)
• I have provided a detailed rationale explaining my changes
• New or modified functions have Ddoc comments (with Params: and Returns:)

Please see CONTRIBUTING.md for more information.

---

If you have addressed all reviews or aren't sure how to proceed, don't hesitate to ping us with a simple comment.

Bugzilla references

Your PR doesn't reference any Bugzilla issue.

If your PR contains non-trivial changes, please reference a Bugzilla issue or create a manual changelog.

Testing this PR locally

If you don't have a local development environment setup, you can use Digger to test this PR:

dub fetch digger
dub run digger -- build "master + phobos#7199"

[CyberShadow]

Worth noting that "Bugs" is a "standard" DDoc section but "Limitations" isn't:

https://dlang.org/spec/ddoc.html#standard_sections

DDoc renders the two a bit differently:

http://dtest.dlang.io/diff/website-4b9608e139d86858b56b33df0deeff2d34c822b1-0a5ced4df5df7b15f158d0f21d39a31b/website-4b9608e139d86858b56b33df0deeff2d34c822b1-4412a24a825aa4718eb7f8ead6eec493/web/phobos-prerelease/std_zip.html

The difference is mainly cosmetic though.