Simplify handling of tuple list (ordering, aggregations)

[Stiivi]

This:

p.sort([["firstname", "asc"]])

looks unintuitive, despite being correct.

Allow:

p.sort("firstname")

This would be nice to have, but should not be allowed as it is ambiguous:

p.sort(["firstname", "asc"])

Does it mean to sort firstname ascending or it means sort by fields firstname and asc in default (ascending) order?