Also, you can create sections named as extension files (e.g. snippets,
preferences and syntaxProfiles) inside user’s Emmet.sublime-settings
file and write your customizations there. See original settings file
for examples.
https://github.com/sergeche/emmet-sublime#extensions-support
self_closing_tag: should empty elements―like br or img―be outputted
with closing dash, boolean. Values are true, false and 'xhtml'
(string; output closing slash in XHTML style, e.g. <br />).
syntaxProfiles.json
http://docs.emmet.io/customization/syntax-profiles/