Move "wiki" into repo

[fulldecent]

This PR moves the wiki into the repo. Wikis as implemented in GitHub do not allow PRs.

That means that after the change:

• Contributors can make pull requests against these pages, e.g. which is the recommended way to link to external implementations.

• We can make changes to the (currently) "wiki" file and the other files at the same time, which is needed to make a complete specification.

How I made this PR

1. Clone open-location-code and open-location-code.wiki
2. Move the wiki inside docs/ in this repo
3. Fix all links

I did NOT make other changes. This is a pure-play pull request. Existing typos, errors are all kept.

How to review and accept this PR

1. Review the files changed link above
2. Click some of the files, check some of the links
3. Merge PR
4. Disable the wiki feature for this repo in project setting (link at top of this page)

Follow on work

1. After this PR is accepted, I will contribute additional PRs to text that was previously in the "wiki".
2. I will invite the PHP implementation to add to our list of external implementations PHP language support #427

[drinckes]

Can you undo this please - I don't want to move the whole wiki into the repo without a discussion.

[fulldecent]

This change did not take effect yet. (It is already "undone".)

The place you are reading this is where we can discuss the topic.

---

As-is, so far, this current proposal is to simply move wiki contents.

This should be the simplest proposal, because after this step, we can then individually talk about other things that can be changed in the wiki and elsewhere.

---

I'm also able to implement/propose slightly more involved changes in this first pass. But then there's a risk that it slows everything down while negotiating it.

[drinckes]

I'll close this as I have moved the wiki files into the repo in another pr.