Comment about CCL syntax modified.

Comment about CCL syntax modified.
(ccl-command-table): Add read-multibyte-character,
write-multibyte-character, and unify-character.
(ccl-code-table): Add ex-cmd.
(ccl-extended-code-table): New variable.
(ccl-embed-extended-command): New function.
(ccl-compile-read-multibyte-character,
ccl-compile-write-multibyte-character,
ccl-compile-unify-character, ccl-compile-iterate-multiple-map,
ccl-compile-translate-multiple-map,
ccl-compile-translate-single-map,
ccl-compile-multiple-map-function) New functions.
(ccl-dump-ex-cmd, ccl-dump-read-multibyte-character,
ccl-dump-write-multibyte-character, ccl-dump-unify-character,
ccl-dump-unify-character-const-tbl, ccl-dump-iterate-multiple-map,
ccl-dump-translate-multiple-map, ccl-dump-translate-single-map):
New functions.