fixed check_simplex and added NaN test
added failing nan test for check_unit_vector
fixed check_unit_vector
added failing NaN test for check_pos_definite
fixed check_pos_definite for NaN values
added another test case for check_pos_definite
added failing NaN test
fixed check_symmetric so it throws for NaNs not on the main diagonal
added doc in the code for check_symmetric
added doc in file for check_simplex
added doc in code for check_unit_vector
added doc in code for check_pos_definite
added failing nan tests for check_pos_semidefinite
added nan check to check_pos_semidefinite and added doc in code
fixed check_pos_semidefinite so it works with 1x1 nan matrix
added NaN test for check_bounded
added doc in code for check_bounded
added NaN test for check_consistent_size
added doc in code for check_consistent_size
added NaN test for check_consistent_sizes