Package is not in the General registry, so `Pkg.add` cannot install it

`SoleFeatures` has no entry in the Julia General registry: `JuliaRegistries/General` has no
`S/SoleFeatures/Versions.toml`. For comparison, `SoleData` has 25 registered versions,
`ModalDecisionTrees` 23, and `SolePostHoc` 2.

So the ordinary way to try this package does not work, and a newcomer has to know to add it by URL.
For an actively developed package, that is a real cost at the first step.

**A second, smaller thing in the same file.** `Project.toml` lists `Revise` in `[deps]`:

```toml
Revise = "295af30f-e4ad-537b-8983-00126c2a3abe"
```

`Revise` is a development tool, so every user installs and precompiles it whether or not they are
developing the package. It normally belongs in `[extras]` with a test target, or in the developer's
own environment. (`MultiData.jl` carries the same line; reported there separately.)

### What would close it

Registering the package, and moving `Revise` out of the runtime dependencies. The two are independent;
either alone is an improvement.

Reported from an outside survey of the ecosystem - happy to open a pull request for the `Revise` half
if useful.