How to map Caps Lock to Escape when tapped and Control when held on Mac OS Sierra

Escape and Control are useful keys when using Vim so it's nice to map them to a more convenient key like Caps Lock. I had been using Karabiner to do this, but Karabiner doesn't work on Mac OS Sierra. Fortunately Karabiner-Elements provides a subset of the features planned for the next generation Karabiner including remapping Caps Lock to Escape when tapped and Control when held down. The solution below is from @zeekay on issue #8. I am using Karabiner-Elements 0.91.12 and macOS Sierra 10.12.4.

• Uninstall Seil and Karabiner, if previously installed
• Install Karabiner-Elements

  $ brew cask install karabiner-elements 
  

• Edit ~/.config/karabiner/karabiner.json to be:

  {
      "global": {
          "check_for_updates_on_startup": true,
          "show_in_menu_bar": true,
          "show_profile_name_in_menu_bar": false
      },
      "profiles": [
          {
              "complex_modifications": {
                  "parameters": {
                      "basic.to_if_alone_timeout_milliseconds": 250
                  },
                  "rules": [
                      {
                          "manipulators": [
                              {
                                  "description": "Change caps_lock to control when used as modifier, escape when used alone",
                                  "from": {
                                      "key_code": "caps_lock",
                                      "modifiers": {
                                          "optional": [
                                              "any"
                                          ]
                                      }
                                  },
                                  "to": [
                                      {
                                          "key_code": "left_control"
                                      }
                                  ],
                                  "to_if_alone": [
                                      {
                                          "key_code": "escape",
                                          "modifiers": {
                                              "optional": [
                                                  "any"
                                              ]
                                          }
                                      }
                                  ],
                                  "type": "basic"
                              }
                          ]
                      }
                  ]
              },
              "devices": [],
              "fn_function_keys": {
                  "f1": "display_brightness_decrement",
                  "f10": "mute",
                  "f11": "volume_decrement",
                  "f12": "volume_increment",
                  "f2": "display_brightness_increment",
                  "f3": "mission_control",
                  "f4": "launchpad",
                  "f5": "illumination_decrement",
                  "f6": "illumination_increment",
                  "f7": "rewind",
                  "f8": "play_or_pause",
                  "f9": "fastforward"
              },
              "name": "Default profile",
              "selected": true,
              "virtual_hid_keyboard": {
                  "caps_lock_delay_milliseconds": 0,
                  "keyboard_type": "ansi"
              }
          }
      ]
  }

Alternative

@kbussell created a script to do the same using Hammerspoon¹ instead of Karabiner.