Allow regular expression in NcML.

[hyoklee]

This is not a bug but an enhancement request. It would be nice if NcML allows regular expression to edit metadata in bulk.

E.g., update units attribute value that has latitude in variable name.

<variable name="/Freeze_Thaw_Retrieval_Data_Polar/latitude.*" shape="lat" type="float">
  <attribute name="units" value="degrees_north" />
</variable>