Stdlib-candidate Reset (#986)

On today's call, we decided to reset stdlib-candidate and start fresh
(and try to manage it more effectively going forward).

This PR is that reset, along with an updated README for the new module.

The main thing that needs reviewing here is the
[README](https://github.com/nushell/nu_scripts/pull/986/files#diff-680b95f9d9e2e9c06ee31ff6835e5d29ba11703ef7252bd42ecafa433767e0c6).

Author: NotTheDr01ds

stdlib-candidate-old/README.md

@@ -0,0 +1,3 @@
+# std-lib candidate
+
+This is the deprecated `stdlib-candidate` module. Please see the [new version](https://github.com/nushell/nu_scripts/tree/main/stdlib-candidate). If you have a submission here, you can move it to the new repo. Please refer to the [README](https://github.com/nushell/nu_scripts/blob/main/stdlib-candidate/README.md) there for the process.

stdlib-candidate-old/nupm.nuon

@@ -0,0 +1,8 @@
+{
+    name: "std-rfc"
+    description: "Official candidates for Nushell standard library"
+    documentation: "https://github.com/nushell/nu_scripts/blob/main/stdlib-candidate/std-rfc/README.md"
+    license: "https://github.com/nushell/nu_scripts/blob/main/LICENSE"
+    version: 0.3.0
+    type: "module"
+}