(chise-tex-accent-macro-alist): New variable.

(chise-tex-accent-macro-alist): New variable.
(chise-tex-encode-region-for-utf-8-jis): Support Greek characters;
don't encode U+00C5 and U+00E5; refer `chise-tex-accent-macro-alist';
use "\'{\^X}" instead of "\CircAcute{X}"; use "\~{\^X}" instead of
"\CircTilde{X}"; add setting for `HornTilde'.
(chise-tex-decode-region): Decode "\={\i}".