OBS elements missing in StationXML

[WayneCrawford]

These are elements important for OBSs but which are not currently in StationXML. If they are not in StationXML we will place them there as Comments, or using an obs-specific namespace. But we can propose them to FDSN as future StationXML additions.

Maybe make a separate document on this?

[WayneCrawford]

clock_correction:
     drift:
        ... *(already specified in standards document)*
     leapseconds:
        ... *(already specified in standards document)*

leveling_system:
    leveling unit: ERI GLC-02
    tolerance : 0.03 degree
    accuracy : 0.01 degree