Add parse_assign_expression() member

Add also parse_or_expression() declaration.
Add parse_or_expression() member

Add also parse_and_expression() declaration.
Add parse_and_expression() member

Add also parse_comparative_expression() declaration.
Add parse_comparative_expression() member

Add also parse_additive_expression() declaration.
Add parse_additive_expression() member

Add also parse_multiplicative_expression() declaration.
Add parse_multiplicative_expression() member

Add also parse_unary_expression() declaration.