Shrink Lisp_Sub_Char_Table by preferring C integers to Lisp_Objects.

Shrink Lisp_Sub_Char_Table by preferring C integers to Lisp_Objects.
* lisp.h (struct Lisp_Sub_Char_Table): Use C integers for depth and
min_char slots.  Adjust comment.
(enum char_table_specials): Rename from CHAR_TABLE_STANDARD_SLOTS.
Add SUB_CHAR_TABLE_OFFSET member.
(make_uninit_sub_char_table): New function.
* alloc.c (mark_char_table): Add extra argument to denote char table
subtype.  Adjust to match new layout of sub char-table.
(mark_object): Always mark sub char-tables with mark_char_table.
* chartab.c (make_sub_char_table, copy_sub_char_table)
(sub_char_table_ref, sub_char_table_ref_and_range, sub_char_table_set)
(sub_char_table_set_range, optimize_sub_char_table, map_sub_char_table)
(map_sub_char_table_for_charset, uniprop_table_uncompress):
All related users changed.
* lread.c (read1): Adjust to match new layout of sub char-table.