+ protos.h. This counts for data typedef's, too! Write one header and
+ one source file per datatype, do proper information hiding and thus
+ provide sane internal abstraction to get "future ready." For example,
+ for all the mailbox handling, the mbox_*/mmdf_* and mh_*/maildir_*
+ functions should only be called directly in the right abstraction
+ layer's implementation. And so forth.