fix string-filter and string-delete argument order

fix string-filter and string-delete argument order

* libguile/srfi-13.h:
* libguile/srfi-13.c (scm_string_filter, scm_string_delete): Swap
  char_pred and s argument order, to comply with SRFI-13. There is a
  back-compat shim that will detect programs that used the old,
  erroneous interface, while giving a warning.

* doc/ref/api-data.texi: Update docs.