made m_graph private.
renamed get_no_vertices(vector2D) to count_vertices(vector2D)
added m_no_vertices property and wrote getter for it, get_no_vertices.
changed stuff everywhere to reflect changes.

changed constructor in base_tsp according to the correct
values for the constraints and dimension of the problem.

added two conversion functions,
from and to decision_vector <-> vector2d<bool>
for convenience. not used currently, problems solved with just 2 loops.

fixed objective function and constraints implementation.

inequality constraints not implemented yet.

test_tsp contains some testing code for obj_fun and constraints_impl
Commented out testing code in test_tsp (will remove later)