patch 8.0.1093: various small quickfix issues

Problem:    Various small quickfix issues.
Solution:   Remove ":" prefix from title set by a user. Add the qf_id2nr().
            function. Add a couple more tests.  Update documentation.
            (Yegappan Lakshmanan)
diff --git a/src/proto/quickfix.pro b/src/proto/quickfix.pro
index ad6ad34..a801edd 100644
--- a/src/proto/quickfix.pro
+++ b/src/proto/quickfix.pro
@@ -22,7 +22,7 @@
 void ex_cfile(exarg_T *eap);
 void ex_vimgrep(exarg_T *eap);
 int get_errorlist(qf_info_T *qi, win_T *wp, int qf_idx, list_T *list);
-int get_errorlist_properties(win_T *wp, dict_T *what, dict_T *retdict);
+int qf_get_properties(win_T *wp, dict_T *what, dict_T *retdict);
 int set_errorlist(win_T *wp, list_T *list, int action, char_u *title, dict_T *what);
 int set_ref_in_quickfix(int copyID);
 void ex_cbuffer(exarg_T *eap);