RFR: Joined the guide into a single file

[Jesper Wilhelmsson]

I have left a forwarding pointer in the old files in case anyone has a link to the guide somewhere. Not sure if this is
needed. Maybe it's better to just remove all the files directly?

I did remove jbslabels.md since that file hasn't been published on the web server yet.

I didn't make any changes in the content except for removing references to getSource.md, hgHelp.md, and tClone.md since
they are outdated and shouldn't be inlined in the guide. I also removed all TBD and sections with no content. Notes has
been added in the todo list in README.md for all sections and TBDs that was removed.

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Commit messages:
 - Merged the guide into a single file

Changes: https://git.openjdk.java.net/guide/pull/28/files
 Webrev: https://webrevs.openjdk.java.net/?repo=guide&pr=28&range=00
  Stats: 3806 lines in 20 files changed: 1477 ins; 2254 del; 75 mod
  Patch: https://git.openjdk.java.net/guide/pull/28.diff
  Fetch: git fetch https://git.openjdk.java.net/guide pull/28/head:pull/28

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