Allow setting custom JSHint options

[peterjosling]

Ace seems to be complaining if I try to set inline options, so there seems to be no way to change the defaults right now.

Might be simplest just to read in from a .jshintrc in the workspace root.

ajaxorg/ace#895 (comment)

[geekgonecrazy]

I'd love this. I've already got .jshintrc files in my project root since brackets takes this.