Discover parameter: time_format and time_composed and time_multicolumn

[abenassi]

• When looking for date values, if something could be parsed by openpyxl directly into datetime.datetime the time format is certain. But if strings have to be evaluated, there should be a strategy to identify if a string could be a date (maybe iterating through the existing date parsing strategies asking for accepts(possible_str_date)). This would probably have to be figured it out together with time_composed (if the string represents a known date format or if it is composed by elements that have to be interpreted to parse a date from them) and time_multicolumn that could hold relevant elements to parse a date in more than one column.