export-ps - a PowerShell variation of export

[RustyF]

This is just a PowerShell version of the export command that creates PowerShell environment variable definitions that you can then feed into Invoke-Expression to yield the same effect at the shell version.

[RustyF]

I went for a super-simple implementation given this is such a small but useful enhancement for PowerShell users. It's a pure extension without touching/refactoring any existing code (besides inserting the command) so that it's a no-brainer to accept.

[jaxxstorm]

Thank you for the contribution!