feat: Add clippy lints

- adds a new 'clippy' category for exercises
- clippy exercises should throw no warnings
- install script now also installs clippy

is related to https://github.com/rust-lang/rust-clippy/issues/2604

install.ps1

@@ -72,14 +72,19 @@ if (!($LASTEXITCODE -eq 0)) {
 # but anyone running pwsh 5 will have to pass the argument.
 $version = Invoke-WebRequest -UseBasicParsing https://api.github.com/repos/rust-lang/rustlings/releases/latest `
     | ConvertFrom-Json | Select-Object -ExpandProperty tag_name
-Write-Host "Checking out version $version..."
-Set-Location $path
-git checkout -q tags/$version
 
 Write-Host "Installing the 'rustlings' executable..."
-cargo install --force --path .
+cargo install --force --git https://github.com/rust-lang/rustlings --tag $version
 if (!(Get-Command rustlings -ErrorAction SilentlyContinue)) {
     Write-Host "WARNING: Please check that you have '~/.cargo/bin' in your PATH environment variable!"
 }
 
+# Checking whether Clippy is installed.
+# Due to a bug in Cargo, this must be done with Rustup: https://github.com/rust-lang/rustup/issues/1514
+$clippy = (rustup component list | Select-String "clippy" | Select-String "installed") | Out-String
+if (!$clippy) {
+    Write-Host "Installing the 'cargo-clippy' executable..."
+    rustup component add clippy
+}
+
 Write-Host "All done! Run 'rustlings' to get started."