Enhance TopN plugin

The current TopN plugin allows selecting the top N rows based on a single field. It would be useful if it could select the top based on ordering multiple fields, with multiple directions. For example:

get the top 10 records ordered by year, month, day
get the top record ordered by age desc, name asc

In addition it looks like not all data types are supported in the plugin, it would be good to enhance it to support more types.

The ordering of null values is also ambiguous, would be good to have an option that specifies if nulls are the top value or bottom value (or maybe just ignored entirely?)