Now Lints Upon Save

Whenever the user saves, the plugin will now automatically run the main `jshint` command.
Merge branch 'master' into on-save
Merge branch 'master' into on-save
Merge
Add settings for automatically linting on edit and save
Add a way of modifying settings
Better way of checking if a file is, in fact, JavaScript
Remove timer after invalidation
Set default options to false
Update readme to describe how automatically linting on edit and save can be enabled
Always reset listener on run