Added an enumerated type of ASCII control character.

[dukc]

No description provided.

[dlang-bot]

Thanks for your pull request and interest in making D better, @dukc! 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 annotated coverage diff directly on GitHub with CodeCov's browser extension
• 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#7010"

[jmdavis]

Given that this is adding a symbol, this will require @andralex's approval - or I guess that it would now require @atilaneves's approval given that he's taking over a lot of what Andrei was doing.

[atilaneves]

What's the main use case?

[dukc]

What's the main use case?

See the latter of two unittests added. This markup is benefitical, because:

1: At least I am more likely to remember meaning of ControlChar.ack than '\x06'
2: If you're using an IDE, you can hit goto definition on ControlChar quicker than you can switch to browser and search for ASCII table. With luck, a tooltip might even directly show you the meaning of control char abbreviation when pointed on (because of the documentation comment on each member of the enum).