Actually add the install script

appveyor/install.ps1

@@ -0,0 +1,85 @@
+# Sample script to install Python and pip under Windows
+# Authors: Olivier Grisel and Kyle Kastner
+# License: CC0 1.0 Universal: http://creativecommons.org/publicdomain/zero/1.0/
+
+$BASE_URL = "https://www.python.org/ftp/python/"
+$GET_PIP_URL = "https://bootstrap.pypa.io/get-pip.py"
+$GET_PIP_PATH = "C:\get-pip.py"
+
+
+function DownloadPython ($python_version, $platform_suffix) {
+    $webclient = New-Object System.Net.WebClient
+    $filename = "python-" + $python_version + $platform_suffix + ".msi"
+    $url = $BASE_URL + $python_version + "/" + $filename
+
+    $basedir = $pwd.Path + "\"
+    $filepath = $basedir + $filename
+    if (Test-Path $filename) {
+        Write-Host "Reusing" $filepath
+        return $filepath
+    }
+
+    # Download and retry up to 5 times in case of network transient errors.
+    Write-Host "Downloading" $filename "from" $url
+    $retry_attempts = 3
+    for($i=0; $i -lt $retry_attempts; $i++){
+        try {
+            $webclient.DownloadFile($url, $filepath)
+            break
+        }
+        Catch [Exception]{
+            Start-Sleep 1
+        }
+   }
+   Write-Host "File saved at" $filepath
+   return $filepath
+}
+
+
+function InstallPython ($python_version, $architecture, $python_home) {
+    Write-Host "Installing Python" $python_version "for" $architecture "bit architecture to" $python_home
+    if (Test-Path $python_home) {
+        Write-Host $python_home "already exists, skipping."
+        return $false
+    }
+    if ($architecture -eq "32") {
+        $platform_suffix = ""
+    } else {
+        $platform_suffix = ".amd64"
+    }
+    $filepath = DownloadPython $python_version $platform_suffix
+    Write-Host "Installing" $filepath "to" $python_home
+    $args = "/qn /i $filepath TARGETDIR=$python_home"
+    Write-Host "msiexec.exe" $args
+    Start-Process -FilePath "msiexec.exe" -ArgumentList $args -Wait -Passthru
+    Write-Host "Python $python_version ($architecture) installation complete"
+    return $true
+}
+
+
+function InstallPip ($python_home) {
+    $pip_path = $python_home + "/Scripts/pip.exe"
+    $python_path = $python_home + "/python.exe"
+    if (-not(Test-Path $pip_path)) {
+        Write-Host "Installing pip..."
+        $webclient = New-Object System.Net.WebClient
+        $webclient.DownloadFile($GET_PIP_URL, $GET_PIP_PATH)
+        Write-Host "Executing:" $python_path $GET_PIP_PATH
+        Start-Process -FilePath "$python_path" -ArgumentList "$GET_PIP_PATH" -Wait -Passthru
+    } else {
+        Write-Host "pip already installed."
+    }
+}
+
+function InstallPackage ($python_home, $pkg) {
+    $pip_path = $python_home + "/Scripts/pip.exe"
+    & $pip_path install $pkg
+}
+
+function main () {
+    InstallPython $env:PYTHON_VERSION $env:PYTHON_ARCH $env:PYTHON
+    InstallPip $env:PYTHON
+    InstallPackage $env:PYTHON wheel
+}
+
+main