vehicles.xml pretty print

[fredshone]

Output xmls are formatted as single strings. In the case of vehicles which is a commonly editted file, it would be useful to have a 'pretty print' option, eg:

        <vehicleType id="Rail">
                <capacity>
                        <seats persons="100"/>
                        <standingRoom persons="0"/>
                </capacity>
                <length meter="200.0"/>
                <width meter="2.8"/>
                <accessTime secondsPerPerson="0.25"/>
                <egressTime secondsPerPerson="0.25"/>
                <doorOperation mode="serial"/>
                <passengerCarEquivalents pce="27.1"/>
        </vehicleType>