Emmet is a web-developer’s toolkit that can greatly improve your HTML & CSS workflow: http://docs.emmet.io
Clone this repo into Brackets extensions folder (can be opened by selecting Help > Show Extensions Folder menu item in Brackets) and restart editor. You should see Emmet menu item with all available actions.
All available keybindings are defined in keymap.json.
To redefine them, simply update keymap.json action values with new keybindings (see CodeMirror Manual for key reference).