That's exactly what I use it for and just set it up yesterday. The instructions on the home page are fairly abysmal though.
1. Create ~/.karabiner.d/configuration/karabiner.json 2. Put some stuff in it (my simple example below) 3. Install the app from the GH page.
Key definitions are in the source code, but if you check the Issues discussion on the Elements project, you'll probably find good examples to send you on your way.
Sample karabiner.json: { "profiles": [ { "name": "Default profile", "selected": true, "simple_modifications": { "right_option": "delete_forward" } } ] }
The next Sierra release might allow the Esc key to be remapped natively, through the Keyboard System Preferences...