Autocomplete improvements

[wojtekmach]

Ref: #985 (comment)

Some ideas here: http://jeremymikkola.com/posts/2019_03_19_rules_for_autocomplete.html

[archdragon]

To keep it simple I would propose:

1. Sorting according to quality where quality = matched chers count/total chars count
2. Prioritising Modules and Functions over Exceptions and Mix Tasks

[josevalim]

Sorting according to quality where quality = matched chers count/total chars count

Agreed.

[josevalim]

Apparently this feature was pushed to the branch already! :D