Delete defining "i" in mule-keymap.

Delete defining "i" in mule-keymap.
(mule-menu-keymap): New variable.  All menu items related to mule
are defined in this keymap.
(set-language-info): Change format of INFO for KEY documentation
and setup-function.
(setup-specified-language-environment): New function.
(setup-language-environment): Call the above function.
(describe-specified-language-support): New function.
(describe-language-support): Call the above function.
(universal-coding-system-argument): New function.
(read-language-and-input-method-name): Doc-string fixed.  If
default-input-method is nil, use previous-input-method as the
default value.
(set-default-input-method): Deleted.