Convert the hexadecimal character code to the corresponding Unicode value.

[Hongyi Zhao]

I noticed some comments on the escape syntax used by Emacs from here
[1-2]. By default, the `describe-char' command will give the code
point representation of the character in hexadecimal and octal
formats, say, #o240, #xa0. So, I want to if there is a convenient way
to do the conversion between the hexadecimal character code
representation and the corresponding Unicode value.

[1] http://ergoemacs.org/emacs/elisp_unicode_representation_in_string.html
[2] (info "(elisp) General Escape Syntax")

Regards, HZ