The only functional change is adding the bang character within
MarkdownFileSettings. That ensures I don't run duplicate the autocommand
and run `silent make` twice upon saving a markdown file. This became
important when I swapped out `shred` for `rm` in my `mdfmt` script
(available in full the commit log message for
e2dbbbbd ).

I no longer need

  autocmd BufNewFile,BufRead *.md,*.markdown set filetype=markdown

because the plasticboy/vim-markdown plugin properly detects markdown
files with either extension.