Solve day thirteen

Minor optimization

Don't grow line if we don't have to.

Make heuristic bound smaller

Solve day twelve

Solve day eleven

Optimize, minor tweaks

Small edit

rustfmt, day 9 description

Solve day 10

Solve day nine

rustfmt

Reduce allocations, don't actually build tree

Solve day eight

Replace HashMap with FxHashMap

cleanup

rustfmt

Solve day seven

Add day 6 description

Solve day six

cargo fmt

Add day 4 and 5 descriptions