Key bindings for UTF-8 encoded characters

Internally characters (keys) have two representations: integers and key
names. Key names are characters strings, usually the name of the
character; e.g., the character A has the representations 65 and "A", and
the tab character the representations 9 and "TAB".

The function keys_int2str() turns the integer representation of a
key/character into the key name.

For display purposes the key names are usually confined to have display
width at most three. Some curses pseudo-keys have longer key names;
e.g., the back-tab character is "KEY_BTAB". A long key name makes a
character difficult to recognize in the status bar menu.

The key name of a multibyte, UTF-8 encoded character is the conventional
Unicode name of the code point; e.g., the character ü has key name
"U+00FC" because ü is the code point 0xFC. Most of these look alike in
the status bar menu.

The patch makes the key name of a multibyte character look like that of
a singlebyte character: the character itself, i.e. the key name of the
character ü is "ü".

The main tool is implementation of a utf8_encode() routine.

Signed-off-by: Lukas Fleischer <lfleischer@calcurse.org>

src/calcurse.h

@@ -1119,6 +1119,7 @@ int utf8_decode(const char *);
 int utf8_width(char *);
 int utf8_strwidth(char *);
 int utf8_chop(char *, int);
+char *utf8_encode(int);
 
 /* utils.c */
 void exit_calcurse(int) __attribute__ ((__noreturn__));