Fix: no-unused-vars to check only file globals (fixes #975)
Merge pull request #981 from roadhump/issue_975

Rule `no-unused-vars` checks only file globals (fixes #975)
Fix: Put rule severity in messages (Fixes #984); deprecates passing full config to Formatters
Merge pull request #985 from jrajav/rule-severity-in-message

Fix: Store rule severity in messages, rather than pulling from the config on-demand