(get_char_code_table): Allow negative character code.

(get_char_code_table): Allow negative character code.
(put_char_code_table): Likewise.
(Vcharacter_composition_table): New variable.
(Q_decomposition): New variable.
(Qwide): New variable.
(Qnarrow): New variable.
(Qcompat): New variable.
(QnoBreak): New variable.
(Qsuper): New variable.
(Qfraction): New variable.
(to_char_code): New function.
(Fget_composite_char): New function.
(Fput_char_attribute): Register `->decomposition' value to
`Vcharacter_composition_table'.
(syms_of_mule_charset): Add new function `get-composite-char', new
symbol `->decomposition', `wide', `narrow', `compat', `noBreak',
`super' and `fraction'.
(vars_of_mule_charset): Setup `Vcharacter_composition_table'.