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 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
Merge branch 'bugfix/issue-898-check-unit-vector-nan' into feature/issue-891-error-checks-nan
added NaN test for check_cholesky_factor_corr
added doc in code for check_cholesky_factor_corr
Merge branch 'bugfix/issue-900-check-pos-finite-nan' into feature/issue-891-error-checks-nan
Merge branch 'feature/issue-891-check-symmetric-nan' into feature/issue-891-error-checks-nan
added NaN test for check_cov_matrix
added doc in code for check_cov_matrix