modularize string arrays for line completion

Instead of using various different forms of string arrays and having to handle them
differently for string completion, we now always use char pointer arrays. This allows
us to remove some large stack allocations, remove a bunch of confusing defines that
keep track of global array sizes, and generally unclutters the code so it's easier
to read.

src/qr_code.c

@@ -142,6 +142,7 @@ int ID_to_QRcode_png(const char *tox_id, const char *outfile)
 
     if (row == NULL) {
         fclose(fp);
+        QRcode_free(qr_obj);
         return -1;
     }