Environment variable `IDD_SAMPLE_DRIVER_CONFIG` for overriding the default config location

Now you can override the default config location C:\IddSampleDriver\option.txt by setting some other file path into IDD_SAMPLE_DRIVER_CONFIG environment variable.
You may need a reboot after changing the value.
The driver works at SYSTEM level, so setting user variables won't have any effect.
No other change.

Remove `CertMgr.exe` dependence

• fix #6
• no changes in functionality

Use option.txt

Use "C:\IddSampleDriver\option.txt" to set the number of monitors and resolutions (doesn't work without this file).
See option.txt .
See https://github.com/roshkins/IddSampleDriver/releases for a basic installation.

Add target modes (~8K)

See https://github.com/roshkins/IddSampleDriver/releases for installation.
Use files in the "for2monitors" folder instead if you want two virtual monitors.