Binding arguments to script parameters.

Added support for passing arguments to scripts that use the param block. So you can run the statement:

    & 'install.ps1' $__rootPath $__toolsPath $__package $__project

With the install.ps1 script below picking up these parameters.

    param($installPath, $toolsPath, $package, $project)

    Write-Host "install.ps1"
    Write-Host $installPath
    Write-Host $toolsPath
    Write-Host $package
    Write-Host $project

Also added support for default parameter values that are constants, e.g.

param($project="MyProject", $count=10)