use (completing-read) instead of (display-completion-list) to complete.

use (completing-read) instead of (display-completion-list) to complete.
so anything.el can benefit from it .
and erl-service.el needn't handle the detail of completing .
(completing-read) can do it itself . for example scroll the \*Completetion\* buffer
the suggested keybinding is bind erl-complete on TAB 
(completing-read) using TAB to scroll \*Completetion\* buffer  ,so you just need press TAB TAB TAB  ..