add rotate (-r) option

[ninewise]

Rotates the two top items on the stack. This allows for some powerful manipulations.

• Wrap a json as a value (add wrap (-w) option #52): echo '{"a":1, "b":2}' | jshon -e a -n object -r -i a2 -i a becomes {"a": {"a2": 1}, "b":2}
• Selecting some items by key (Extract and insert into new object #55): echo '{"a":1, "b":2, "c":3}' | jshon -e a -r -e b -r -p -n object -r -i b -r -i a becomes {"b":2, "a":1}