Fix compiler flags
Fix code style issues
[3/3] Implement brute-force solver

Small code-cleanups and fix for a ugly leak
Remove unused Callback feature from solvers
Small optimizations
Replace C-style headers with Cpp-style headers
Rename Board::usedCells to Board::count
[1/4] Add "Only this cell can be X" verification to BillSolver

This first commit only looks through the rows (or columns, depending on your POV =P)
[2/4] Add "Only this cell can be X" verification to BillSolver

Now it also checks if it's the only possibility on the column (or row, depending on your POV =P)
FINALLY fix the Makefile's dependency problem
Makefile: Remove the unused "todo" target