Implement 'scm_c_bind_keyword_arguments'.

Implement 'scm_c_bind_keyword_arguments'.

* libguile/keywords.c (scm_keyword_argument_error): New variable.
  (scm_c_bind_keyword_arguments): New API function.

* libguile/keywords.h (enum scm_keyword_arguments_flags): New enum.
  (scm_t_keyword_arguments_flags): New typedef.
  (scm_c_bind_keyword_arguments): New prototype.

* doc/ref/api-data.texi (Coding With Keywords, Keyword Procedures): Add
  documentation.

* test-suite/standalone/test-scm-c-bind-keyword-arguments.c: New file.

* test-suite/standalone/Makefile.am: Add
  test-scm-c-bind-keyword-arguments test.