(GH-1060) Add BeforeInstall parameter to Install-ChocolateyPackage.ps1

- Add a ScriptBlock parameter `BeforeInstall` to Install-ChocolateyPackage.ps1. If supplied, the script block is called after download but before install.

src/chocolatey.resources/helpers/functions/Install-ChocolateyPackage.ps1

@@ -220,6 +220,13 @@ functionality (see links).
 .PARAMETER IgnoredArguments
 Allows splatting with arguments that do not apply. Do not use directly.
 
+.PARAMETER BeforeInstall Script
+Specifies the commands to run after download has completed but before install steps have begun.
+Available in 0.10.16+.
+
+Use this for starting an auxilary process such as AutoHotkey, so that any timeouts are not 
+affected by the time to download.
+
 .EXAMPLE
 >
 $packageName= 'bob'
@@ -359,6 +366,8 @@ param(
   [parameter(Mandatory=$false)]
   [alias("useOnlyPackageSilentArgs")][switch] $useOnlyPackageSilentArguments = $false,
   [parameter(Mandatory=$false)][switch]$useOriginalLocation,
+  [parameter(Mandatory=$false)]
+  [scriptblock] $beforeInstall,
   [parameter(ValueFromRemainingArguments = $true)][Object[]] $ignoredArguments
 )
   [string]$silentArgs = $silentArgs -join ' '
@@ -405,6 +414,10 @@ param(
                                       -GetOriginalFileName
   }
 
+  if ($beforeInstall) {
+    & $beforeInstall
+  }
+
   Install-ChocolateyInstallPackage -PackageName $packageName `
                                    -FileType $fileType `
                                    -SilentArgs $silentArgs `