Option to hint JS files on load

The vim module [vim-jshint](https://github.com/Shutnik/jshint2.vim#configuration) can optionally hint JS files on **open** as well as on **save**. I found this to be a handy setting so I've added the same ability to Sublime-JSHint in this PR.

Test and works fine in ST2; in ST3, tho, nothing happens. Any suggestions?