Modification of checker_board.hpp

Have the print_board function going through the map to get the active
pieces on the board.
Modified checker_board.hpp and tests.cpp

Redid the base container of the board to a 2D vector of characters.
Modifications to checker_board.hpp and tests.cpp

Refactoring the piece moving code, failing tests to jump pieces.
Modified checker_board.hpp and tests.cpp

Passing all the tests currently. Require to do further testing on the
king jumps.
Modified tests.cpp

Consolidated some of the test cases.
Modification of checker_board and tests. Adding minimax.hpp.

Have the checker board generating all the possible moves for the pieces
and have the test cases in place.

Added a new file minimax to start having the search algorithm for the
game search.