Add some way to quickly import std modules

[CGQAQ]

For example: after I type https://deno.land/std@, give me completions of all std lib versions out there; and when I select a version and hit tab, give me completions of all std module in here

And of course, add a snippet code for example importstd, hit tab key give me import {<2. hit tab input here>} from 'https://deno.land/std@<1. input here>'

[CGQAQ]

cc @ry