GETPROP get property values from label list

      ALLVAL=GETPROP(LAB,PROP)
      VAL=GETPROP(LAB,PROP,CATEGORY)

 INPUT
    LAB        SDLAB object whose list is used
    PROP       property name
    CATEGORY   category specification (name, index or reg.exp)

 OUTPUT
    VAL        single value
    ALLVAL     cell array with values for all categories

 DESCRIPTION
 GETPROP retrieves value(s) of a label list property PROP. If no CATEGORY
 is specified, GETPROP returns cell array ALLVAL with all per-category
 values. If a CATEGORY is given, only one value is returned. CATEGORY
 needs to point to a single entry in the LIST.

 EXAMPLES
 GETPROP(LAB,'marker')    % return cell array with all markers
 GETPROP(LAB,'marker','banana')  % return marker for 'banana'

 SEE ALSO
 SETPROP, ISPROP, RMPROP, GETPROPLIST