* Replace direct `fmt.Println()` usage in a test with `t.Log()`
* Rename `cmd` to `cli`
* Move asdf command from module root
* Fix some linter warnings, thus enabling some tests that were being skipped
* Fix `Makefile`
* Rename module to `github.com/asdf-vm/asdf`
* Fix `TestGetAllToolsAndVersionsInContent/returns_empty_list_with_found_true_and_no_error_when_empty_content`
* Rewrite `Unique()` to be a bit more straightforwards
* Get workflow checks passing again
toolversions.Unique is ever so slightly faster, technically.
```
goos: linux
goarch: amd64
pkg: github.com/asdf-vm/asdf/internal/toolversions
cpu: AMD Ryzen 9 3900X 12-Core Processor
│ /tmp/old.txt │ /tmp/new.txt │
│ sec/op │ sec/op vs base │
Unique-24 346.5n ± 1% 342.4n ± 1% -1.17% (p=0.027 n=10)
│ /tmp/old.txt │ /tmp/new.txt │
│ B/op │ B/op vs base │
Unique-24 160.0 ± 0% 160.0 ± 0% ~ (p=1.000 n=10) ¹
¹ all samples are equal
│ /tmp/old.txt │ /tmp/new.txt │
│ allocs/op │ allocs/op vs base │
Unique-24 3.000 ± 0% 3.000 ± 0% ~ (p=1.000 n=10) ¹
¹ all samples are equal
```
* Add `x/sys` as a dependency
* Create `toolversions.Unique` function
* Create `shims` package with `ExecutablePaths`, `PluginExecutables`, `Write`, `GenerateForVersion` function
* Address linter warnings
Some of the Go tests actually cloned remote repos, which meant slow tests, and tests failures if I was working offline. These changes allow all Go tests to run offline. The test code now clones local Git repos instead of remotes ones.
* Add otiai10/copy as a dependency
* Create repotest package for test code that needs to work with Git repos
* Add back missing test script for execute package
* Update git, pluginindex, and plugins package tests so they work offline
* Add go-git as a dependency
* Remove plugins dir from gitignore
* Move config code to config package
* Create validatePluginName function
* Create PluginDirectory function
* Create PluginExists function
* Implement PluginAdd function
* Add testify as a dependency
* Write test for PluginAdd happy path
* rename commands package to cmd
* add go-ini as a dependency
* write code to parse asdfrc file into Settings struct
* add go-envconfig as a dependency
* add go-homedir as a dependency
* implement first version of LoadConfig function to load environment variables into Config struct
