Add ability to specify log facility per-command

[leojackson]

Currently, whether a set of commands is logged depends on the log level assigned in the module. This implies that the specified Write-* function is hierarchically connected to other Write-* functions, which isn't actually the case in PowerShell; the hierarchy is implied by the enum PsLogLiteLevel.

Ideally, the function would be able to turn logging on and off per function, so you could enable it, for example, for Write-Debug and Write-Warning but not Write-Error or Write-Output. The "Log Level" could be kept as a shortcut to turn certain functions on and off.