DRY out my Vim ftdetects

I knew there was a way to do this properly.  The FileType event was the
key.

http://vimdoc.sourceforge.net/htmldoc/filetype.html
http://vimdoc.sourceforge.net/htmldoc/autocmd.html#FileType
http://vimdoc.sourceforge.net/htmldoc/autocmd.html#autocmd-events