Use from_scm and to_scm for booleans
For consistency, eliminate ly_bool2scm and ly_scm2bool. Also replace use of scm_from_boolean. ly_scm2bool replaced with scm_is_true. ly_bool2scm and scm_from_boolean become from_scm, ensuring each time that the argument is a boolean and not something implicitly convertible to a boolean; for pointers, static casts are added to that effect.
Relatedly, remove the unused function ly_scm2char
.
Edited by Jean Abou Samra