Add 'Go To Definition' Support

[joefitzgerald]

It would be nice to have a keyboard shortcut / right click menu item / menu item to go to definition for the current cursor position.

[joefitzgerald]

... or go oracle: https://atom.io/packages/go-oracle

[joefitzgerald]

See #24.

[nathany]

FYI: In Sublime Text 3, this is Cmd-Option-down (cross-language, possibly ctags or something like it). There are also Jump Back and Jump Forward to use alongside this or other forms of navigation.