Add install.ps1 for downloading fzf.exe on Windows (junegunn#1845)

install.ps1

@@ -0,0 +1,73 @@
+$version="0.20.0"
+
+if ([Environment]::Is64BitProcess) {
+  $binary_arch="amd64"
+} else {
+  $binary_arch="386"
+}
+
+$fzf_base=Split-Path -Parent $MyInvocation.MyCommand.Definition
+
+function check_binary () {
+  Write-Host "  - Checking fzf executable ... " -NoNewline
+  $output=cmd /c $fzf_base\bin\fzf.exe --version 2>&1
+  if (-not $?) {
+    Write-Host "Error: $output"
+    $binary_error="Invalid binary"
+  } else {
+    $output=(-Split $output)[0]
+    if ($version -ne $output) {
+      Write-Host "$output != $version"
+      $binary_error="Invalid version"
+    } else {
+      Write-Host "$output"
+      $binary_error=""
+      return 1
+    }
+  }
+  Remove-Item "$fzf_base\bin\fzf.exe"
+  return 0
+}
+
+function download {
+  param($file)
+  Write-Host "Downloading bin/fzf ..."
+  if ("$version" -ne "alpha") {
+    if (Test-Path "$fzf_base\bin\fzf.exe") {
+      Write-Host "  - Already exists"
+      if (check_binary) {
+        return
+      }
+    }
+  }
+  if (-not (Test-Path "$fzf_base\bin")) {
+    md "$fzf_base\bin"
+  }
+  if (-not $?) {
+    $binary_error="Failed to create bin directory"
+    return
+  }
+  cd "$fzf_base\bin"
+  if ("$version" -eq "alpha") {
+    $url="https://github.com/junegunn/fzf-bin/releases/download/alpha/$file"
+  } else {
+    $url="https://github.com/junegunn/fzf-bin/releases/download/$version/$file"
+  }
+  $temp=$env:TMP + "\fzf.zip"
+  [Net.ServicePointManager]::SecurityProtocol = [Net.SecurityProtocolType]::Tls12
+  (New-Object Net.WebClient).DownloadFile($url, $ExecutionContext.SessionState.Path.GetUnresolvedProviderPathFromPSPath("$temp"))
+  if ($?) {
+    (Expand-Archive -Path $temp -DestinationPath .); (Remove-Item $temp)
+  } else {
+    $binary_error="Failed to download with powershell"
+  }
+  if (-not (Test-Path fzf.exe)) {
+    $binary_error="Failed to download $file"
+    return
+  }
+  check_binary >$null
+}
+
+download "fzf-$version-windows_$binary_arch.zip"
+
+Write-Host 'For more information, see: https://github.com/junegunn/fzf'