RFR: Joined the guide into a single file

[Jesper Wilhelmsson]

On Fri, 9 Oct 2020 20:45:17 GMT, Andreas Lundblad <github.com+5994243+aioobe at openjdk.org> wrote:

> I see a lot of deletions and few additions. Surely some content has been removed?

No actual content should have been removed. If so, that is a bug. The parts that have been removed are:

* Prev - TOC - Next  -links on top and bottom of each page
* The index is now automatically generated
* Sections with no actual content like bugDatabase.md has been removed and gotten a note in the todo-list in the readme
* faq.md was removed since it explicitly said that it was a temporary holder for questions that were to be answered in
  the guide - now replaced by the todo-list

Depending on what metric you use to count deletions and additions a contributing factor could be that I have removed a
lot of linebreaks.

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PR: https://git.openjdk.java.net/guide/pull/28