A new MODE tool is to be created to perform arbitrary set operations
(union, intersection, difference, etc.) on objects generated by MODE.
The objects in general will be associated with different variables.
Object attributes (centroid, axis, etc.) will be computed for the resultant objects.
Matching and merging may be a later option.
This tool is to be tested on fields relevant for dryline identification
(gradient of temperature, gradient of specific humidity, etc.).
The output format of the new tool will be identical to that of MODE.

Account Key: 2700042 WPC

Related METplus issue: dtcenter/METplus#1516