Enable multiline input

Adds a nonl() call to avoid translation from \r to \n when pressing
enter.
C-J -> \n
Enter -> \r
To allow multiline input, \n chars (e.g. when pressing C-J) are replaced
with a pilcrow. After hitting enter, every pilcrow is substituted with
\n again.

src/misc_tools.h

@@ -78,6 +78,9 @@ void update_unix_time(void);
 /* Returns 1 if the string is empty, 0 otherwise */
 int string_is_empty(const char *string);
 
+/* Same as above but for wide character strings */
+int wstring_is_empty(const wchar_t *string);
+
 /* convert a multibyte string to a wide character string (must provide buffer) */
 int char_to_wcs_buf(wchar_t *buf, const char *string, size_t n);