edit: tweak default editors.

Add `atom` (not my editor of choice [TextMate for life!]) but widely
used enough to probably warrant it. Also, reorder based on my best
guestimates of current usage and cleanup the editor code while we're
here.

Library/Homebrew/dev-cmd/edit.rb

@@ -21,8 +21,8 @@ module Homebrew
     # If no brews are listed, open the project root in an editor.
     if ARGV.named.empty?
       editor = File.basename which_editor
-      if ["mate", "subl"].include?(editor)
-        # If the user is using TextMate or Sublime Text,
+      if ["atom", "subl", "mate"].include?(editor)
+        # If the user is using Atom, Sublime Text or TextMate
         # give a nice project view instead.
         exec_editor HOMEBREW_REPOSITORY/"bin/brew",
                     HOMEBREW_REPOSITORY/"README.md",

Library/Homebrew/utils.rb

@@ -328,21 +328,16 @@ def which_all(cmd, path = ENV["PATH"])
 end
 
 def which_editor
-  editor = ENV.values_at("HOMEBREW_EDITOR", "HOMEBREW_VISUAL").compact.reject(&:empty?).first
-  return editor unless editor.nil?
+  editor = ENV.values_at("HOMEBREW_EDITOR", "HOMEBREW_VISUAL")
+              .compact
+              .reject(&:empty?)
+              .first
+  return editor if editor
 
-  # Find Textmate, BBEdit / TextWrangler, or vim
-  %w[mate edit vim].each do |candidate|
-    editor = candidate if which(candidate, ENV["HOMEBREW_PATH"])
+  # Find Atom, Sublime Text, Textmate, BBEdit / TextWrangler, or vim
+  editor = %w[atom subl mate edit vim].find do |candidate|
+    candidate if which(candidate, ENV["HOMEBREW_PATH"])
   end
-
-  # Find Textmate
-  editor = which("mate", ENV["HOMEBREW_PATH"])
-  # Find BBEdit/TextWrangler
-  editor ||= which("edit", ENV["HOMEBREW_PATH"])
-  # Find vim
-  editor ||= which("vim", ENV["HOMEBREW_PATH"])
-  # Default to standard vim
   editor ||= "/usr/bin/vim"
 
   opoo <<-EOS.undent