Allow sorting of output fields

[varac]

If would be great to be able to sort the fields that are put together as description.
I.e. my bank transactions csv file have the sender and description at fields 10+11, and I'd like to put all the other fields behind them, like

reckon --output-fields 10,11,6,4,8,1,3 ...

[cantino]

We're open to pull requests :)