Implement trap statement

    trap { 'trapped' }
    trap { continue }
    trap { break }
    trap { $_.Exception.Message }
    trap [System.FormatException] { }

Break and continue as child statements inside the trap body currently do not work, for example:

    trap {
        if {$continueOnError) {
            continue
        }
    }

$_ is not currently written to the error stream since that does not seem to be output to the host.