(ids-update-index): New optional argument `in-memory'; if it is

(ids-update-index): New optional argument `in-memory'; if it is
specified, don't save `ideographic-products'.
(ideographic-character-get-structure): New function.
(ideographic-char-match-component): New function.
(ideographic-structure-char<): New function.
(ideographic-chars-to-is-a-tree): New function.
(ids-find-chars-including-ids*): New function.
(ids-find-chars-including-ids): New function.
(functional-ideographic-structure-to-apparent-structure): New
function.
(ideographic-structure-compact): Moved from ids-rw.el; use
`ideographic-structure-find-chars' instead of
`ideographic-structure-find-char'.