vim:setts: Deactivate 'relativenumber'

I rarely use them and are more an annoyance.

For the case that I want to enable them in a session, move the
numbertoggle augroup into a function and add an autocommand on
`OptionSet relativenumber`.

.config/vim/vimrc.d/30-settings.vim

@@ -1,11 +1,21 @@
 " Settings """""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""
-" hybrid linenumbers
-set number relativenumber
-augroup numbertoggle
-	au!
-	au BufEnter,FocusGained,InsertLeave,WinEnter * if &nu | set rnu   | endif
-	au BufLeave,FocusLost,InsertEnter,WinLeave   * if &nu | set nornu | endif
-augroup END
+
+" linenumbers
+set number
+" If relative linenumbers are activated, have them only in the focused window
+function! Numbertoggle()
+	augroup numbertoggle
+		au!
+		au OptionSet relativenumber call Numbertoggle()
+
+		if &relativenumber
+			au BufEnter,FocusGained,InsertLeave,WinEnter * if &nu | set rnu   | endif
+			au BufLeave,FocusLost,InsertEnter,WinLeave   * if &nu | set nornu | endif
+		endif
+	augroup END
+endfunction
+call Numbertoggle()
+
 " no timeout when exiting insert-mode
 " (see https://www.johnhawthorn.com/2012/09/vi-escape-delays/)
 set timeoutlen=1000 ttimeoutlen=0