Changes for version 0.14
- Had set the weed-out-expensive-solutions cost at the start of the loop at 2**width, wrongly thinking that that would be the maximum cost. Found a couple cases where that's not true, making solve() return them as "()". Put those cases in a new test file 27-solve.t.
- Changed the weeding-out code to use an actual cost from the covers array for the starting value.