Add method to KeysFile for getting github users

* This returns a list of only the github users which have been added to
  your keys file.

Author: iamvery

lib/github/auth/keys_file.rb

@@ -31,6 +31,12 @@ def delete!(keys)
       write_keys_file { |keys_file| keys_file.write new_content }
     end
 
+    def github_users
+      # http://rubular.com/r/2LjIGaKObz
+      regex = %r{github\.com/(.+)}
+      keys_file_content.scan(regex).flatten.uniq.sort
+    end
+
     private
 
     def append_keys_file(&block)

spec/unit/github/auth/keys_file_spec.rb

@@ -197,4 +197,22 @@
       end
     end
   end
+
+  describe '#github_users' do
+    let(:keys) {[
+      Github::Auth::Key.new('jay',   'abc123'),
+      Github::Auth::Key.new('chris', 'def456'),
+      Github::Auth::Key.new('chris', 'ghi789'),
+    ]}
+
+    before do
+      keys_file.write keys.join("\n")
+      keys_file.write "\n"
+      keys_file.rewind
+    end
+
+    it 'returns a uniq, ordered list of github users' do
+      expect(subject.github_users).to eq(%w(chris jay))
+    end
+  end
 end