Start Pash with commands as arguments

These commits add a non-interactive mode for Pash.
You can now directly pass commands as arguments to the PashConsole. In addition, the "-noexit" specifier can be added in order to not exit after executing the provided commands and switching to the interactive mode. It's now for example possible to simply execute a Pash script, without using the interactive prompt.

Tests were added that test the FullHost.Run() methods and the PashConsole in a separate process.

The implemented behavior matches the behavior of Powershell on Windows.