Add record objects with user-defined types.

Add record objects with user-defined types.

* src/alloc.c (allocate_record): New function.
(Fmake_record, Frecord, Fcopy_record): New functions.
(syms_of_alloc): defsubr them.
(purecopy): Work with records.

* src/data.c (Ftype_of): Return slot 0 for record objects, or type
name if record's type holds class.
(Frecordp): New function.
(syms_of_data): defsubr it.  Define `Qrecordp'.
(Faref, Faset): Work with records.

* src/fns.c (Flength): Work with records.

* src/lisp.h (prec_type): Add PVEC_RECORD.
(RECORDP, CHECK_RECORD, CHECK_RECORD_TYPE): New functions.

* src/lread.c (read1): Add syntax for records.

* src/print.c (PRINT_CIRCLE_CANDIDATE_P): Add RECORDP.
(print_object): Add syntax for records.

* test/lisp/emacs-lisp/cl-print-tests.el (cl-print-tests-2):
New test.

* test/src/alloc-tests.el (record-1, record-2, record-3):
New tests.

* doc/lispref/elisp.texi, doc/lispref/objects.texi,
doc/lispref/records.texi: Add documentation for records.