Add support for "InstallDir"

[mottosso]

I noticed the install directory was hard-coded to ProgramFilesFolder.

With this PR, users can install to a directory other than ProgramFilesFolder, such as PersonalFolder. It think it may even work with juts about any Property, but I'm not well versed enough with MSI to know for sure.

Example

{
    "Name": "My App",
    "UpgradeCode": "CFDD2143-B60A-4F5E-A81B-E1481DA674E1",
    "Version": "1.0.0",
    "Manufacturer": "Acme",
    "Description": "My Acme app",
    "InstallDir": "PersonalFolder",
    "...": "..."
}

[sk1project]

@mottosso did you check this one on MSI installation level? We have tested (not with your patch) custom root folder for installation and got errors on MSI execution.

[mottosso]

Thanks for getting back.

did you check this one on MSI installation level?

Do you mean if I've tried installing an MSI generated with this addition? Yes, I'm using this successfully as we speak.

[sk1project]

Great! We will test this patch and merge it!