Add clarity for not-implemented functions

[PaulWalkerUK]

I'd like to do something to the functions that aren't implemented yet, to make it more obvious for anyone wanting to use this module exactly what it can/can't currently do. I'm wondering about maybe either:

• Commenting them out of the module manifest so they're not exported (the README.md would need tweaking)
• Add a Write-Error to the functions and change the help text to make it clear they're not implemented

I'm happy to make these changes and submit a pull request, just wondered if you had any thoughts or preferences about it?