chore: Significantly restructure folder layout

This moves the various projects from "type-based" folders (such as
"services" or "tools") into more appropriate semantic folders (such as
"nix", "ops" or "web").

Deprecated projects (nixcon-demo & gotest) which only existed for
testing/demonstration purposes have been removed.

(Note: *all* builds are broken with this commit)

docs/CODE_OF_CONDUCT.md

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+A SERMON ON ETHICS AND LOVE
+===========================
+
+One day Mal-2 asked the messenger spirit Saint Gulik to approach the
+Goddess and request Her presence for some desperate advice. Shortly
+afterwards the radio came on by itself, and an ethereal female Voice
+said **YES?**
+
+"O! Eris! Blessed Mother of Man! Queen of Chaos! Daughter of Discord!
+Concubine of Confusion! O! Exquisite Lady, I beseech You to lift a
+heavy burden from my heart!"
+
+**WHAT BOTHERS YOU, MAL? YOU DON'T SOUND WELL.**
+
+"I am filled with fear and tormented with terrible visions of pain.
+Everywhere people are hurting one another, the planet is rampant with
+injustices, whole societies plunder groups of their own people,
+mothers imprison sons, children perish while brothers war. O, woe."
+
+**WHAT IS THE MATTER WITH THAT, IF IT IS WHAT YOU WANT TO DO?**
+
+"But nobody Wants it! Everybody hates it."
+
+**OH. WELL, THEN *STOP*.**
+
+At which moment She turned herself into an aspirin commercial and left
+The Polyfather stranded alone with his species.
+
+SINISTER DEXTER HAS A BROKEN SPIROMETER.

docs/CONTRIBUTING.md

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+Contribution Guidelines
+=======================
+
+<!-- markdown-toc start - Don't edit this section. Run M-x markdown-toc-refresh-toc -->
+**Table of Contents**
+
+- [Contribution Guidelines](#contribution-guidelines)
+    - [Before making a change](#before-making-a-change)
+    - [Commit messages](#commit-messages)
+    - [Commit content](#commit-content)
+    - [Code quality](#code-quality)
+    - [Builds & tests](#builds--tests)
+
+<!-- markdown-toc end -->
+
+This is a loose set of "guidelines" for contributing to my depot. Please note
+that I will not accept any patches that don't follow these guidelines.
+
+Also consider the [code of conduct](CODE_OF_CONDUCT.md). No really, you should.
+
+## Before making a change
+
+Before making a change, consider your motivation for making the change.
+Documentation updates, bug fixes and the like are *always* welcome.
+
+When adding a feature you should consider whether it is only useful for your
+particular use-case or whether it is generally applicable for other users of the
+project.
+
+When in doubt - just ask! You can reach out to me via
+[mail](mailto:mail@tazj.in) or on Twitter / IRC / etc.
+
+## Commit messages
+
+All commit messages should be structured like this:
+
+```
+type(scope): Subject line with at most a 68 character length
+
+Body of the commit message with an empty line between subject and
+body. This text should explain what the change does and why it has
+been made, *especially* if it introduces a new feature.
+
+Relevant issues should be mentioned if they exist.
+```
+
+Where `type` can be one of:
+
+* `feat`: A new feature has been introduced
+* `fix`: An issue of some kind has been fixed
+* `docs`: Documentation or comments have been updated
+* `style`: Formatting changes only
+* `refactor`: Hopefully self-explanatory!
+* `test`: Added missing tests / fixed tests
+* `chore`: Maintenance work
+
+And `scope` should refer to some kind of logical grouping inside of the project.
+
+Please take a look at the existing commit log for examples.
+
+## Commit content
+
+Multiple changes should be divided into multiple git commits whenever possible.
+Common sense applies.
+
+The fix for a single-line whitespace issue is fine to include in a different
+commit. Introducing a new feature and refactoring (unrelated) code in the same
+commit is not fine.
+
+`git commit -a` is generally **taboo**.
+
+In my experience making "sane" commits becomes *significantly* easier as
+developer tooling is improved. The interface to `git` that I recommend is
+[magit][]. Even if you are not yet an Emacs user, it makes sense to install
+Emacs just to be able to use magit - it is really that good.
+
+For staging sane chunks on the command line with only git, consider `git add
+-p`.
+
+## Code quality
+
+This one should go without saying - but please ensure that your code quality
+does not fall below the rest of the project. This is of course very subjective,
+but as an example if you place code that throws away errors into a block in
+which errors are handled properly your change will be rejected.
+
+In my experience there is a strong correlation between the visual appearance of
+a code block and its quality. This is a simple way to sanity-check your work
+while squinting and keeping some distance from your screen ;-)
+
+## Builds & tests
+
+My projects are built using [Nix][] to avoid "build pollution" via the user's
+environment.
+
+If you have Nix installed and are contributing to a project tracked in this
+repository, you can usually build the project by calling `nix-build -A
+path.to.project`.
+
+For example, to build a project located at `tools/foo` you would call `nix-build
+-A tools.foo`
+
+If the project has tests, check that they still work before submitting your
+change.
+
+## Submitting patches
+
+When making a change, please create an appropriate commit locally and send it to
+me using either `git send-email` or `git format-patch`. The email address to use
+for depot reviews is `reviews@tazj.in`, which is a [public group][].
+
+I recognise that most people are used to a GitHub-style workflow. If you run
+into issues with the above but would still like to contribute, feel free to
+reach out to me.
+
+[magit]: https://magit.vc/
+[Nix]: https://nixos.org/nix/
+[public group]: https://groups.google.com/a/tazj.in/forum/#!forum/reviews