Add diff-hl package
Merge branch 'master' of github.com:bbatsov/prelude

Conflicts:
	core/prelude-editor.el
Save all buffers on focus lost
Recognize Elixir source files automatically
Recognize Rust source files automatically
Merge remote-tracking branch 'upstream/master'

* upstream/master:
  Recognize Rust source files automatically
  Recognize Elixir source files automatically
  Save all buffers on focus lost
  Add diff-hl package