Add support for eslint_d

[roman01la]

eslint_d support just landed in SublimeLinter-eslint.
Can we have it in this package?
Maybe like another option: Use eslint_d.

[rosston]

There should be little to no performance benefit to using eslint_d over the current method. eslint_d's key performance gain is in not starting up a new node process, but this package already avoids that problem by using eslint's CLIEngine module from within Atom's (already running) node process.

[roman01la]

@rosston Didn't know about that. Thanks!

[mantoni]

Yes, this is important to know. I've added a note for Atom users to the eslint_d readme.