build: create XML documentation file on build and copy it to both binary output directories

[laolubenson]

What types of changes are you proposing/introducing to the .NET client?

Put an x in the boxes that apply

• Bugfix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• New feature (non-breaking change which adds value to the project)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)

Details

Create XML documentation file on build and copy it to both binary output directories. Currently a file is created in the project root folder instead of the binary output directory.

closes #441