put string helpers in own file

src/toxic_strings.h

@@ -0,0 +1,31 @@
+/*
+ * Toxic -- Tox Curses Client
+ */
+
+/* Adds char to buffer at pos */
+void add_char_to_buf(wchar_t *buf, size_t *pos, size_t *len, wint_t ch);
+
+/* Deletes the character before pos */
+void del_char_buf_bck(wchar_t *buf, size_t *pos, size_t *len);
+
+/* Deletes the character at pos */
+void del_char_buf_frnt(wchar_t *buf, size_t *pos, size_t *len);
+
+/* Deletes the line from beginning to pos */
+void discard_buf(wchar_t *buf, size_t *pos, size_t *len);
+
+/* Deletes the line from pos to len */
+void kill_buf(wchar_t *buf, size_t *pos, size_t *len);
+
+/* nulls buf and sets pos and len to 0 */
+void reset_buf(wchar_t *buf, size_t *pos, size_t *len);
+
+/* looks for the first instance in list that begins with the last entered word in buf according to pos, 
+   then fills buf with the complete word. e.g. "Hello jo" would complete the buffer 
+   with "Hello john".
+
+   list is a pointer to the list of strings being compared, n_items is the number of items
+   in the list, and size is the size of each item in the list. 
+
+   Returns the difference between the old len and new len of buf on success, -1 if error */
+int complete_line(wchar_t *buf, size_t *pos, size_t *len, const void *list, int n_items, int size);