[Feature Request] PowerShell interpolation

[0x7FFFFFFFFFFFFFFF]

Right now we can do command interpolation like

`!v strftime("%c")`

or shell interpolation like

`whoami`

On Windows, shell interpolation is calling the old-school batch command. Is it possible to add PowerShell interpolation like

`!ps Get-Process | Sort-Object -Descending cpu | Select-Object -First 5`

Considering PowerShell is much powerful than the old-school batch command and it's cross-platform now, it would be cool to have this in UltiSnip.