Fix for bad Windows shell integration

[WillEhrendreich]

the setup process doesn't integrate with the shell properly.

trying to open with the context menu gives this error dialog

i found the problem, after a bit.

the registry value it gives ends up having a slash before the filepath to fvim so it would be something like "\C:\Fvim\Fvim.exe" "%1" instead of "C:\Fvim\Fvim.exe" "%1"

changing to the second version in my registry editor does actually fix the problem.