* Rename `versions.Installed` function to `IsInstalled`
* Create `versions.Installed` function
* Create `shims.GenerateForPluginVersions` and `shims.GenerateAll` functions
* Address linter warnings
* Create asdf reshim command
* Run asdf hook from new `shims` functions
* Add `x/sys` as a dependency
* Create `toolversions.Unique` function
* Create `shims` package with `ExecutablePaths`, `PluginExecutables`, `Write`, `GenerateForVersion` function
* Address linter warnings
* Get asdf info BATS tests working
* Create `versions.Installed` function
* Update `versions.Latest` to return single version
* Implement `latest` asdf command