feat: use recommended solver

[hubcity]

[hubcity/fplan#9]

[wscott]

Interesting. For me, this change names the output "cleaner" and less random looking and generates the same level of living expenses, but the final amount paid for taxes is higher:

-total spending: 15876539
-total tax: 1984385 (12.5%)
+total spending: 15829379
+total tax: 2131504 (13.5%)

I am pretty sure this is why the change to avoid Roth conversions didn't work when I tried it in my tree.

[wscott]

I thought about this and realized that we don't tell it to minimize taxes and as long as the spending is maximized both solutions are good.

I muse about how to fix this in #17.

So I am going to accept this one as is.