PRINTSTRUCT | Recursively print structures to the command window or a cell char array

Recursively print hierarchical outline of structure contents. This is a minor adaptation of the File Exchange contribution "Structure outline" written by B. Roossien. Changes include:
- automatic determination of input structure variable name, which is used to title each struct
- included output argument that, when defined, returns the printed struct as char cell array and suppresses output to command window
- input specification and defining default values is easier and more flexible
- (possibly) better handling of structure arrays