Fix the issue that the vim config would always be reloaded on save
(jumping to the BOF; another TODO) even in non `*.vim` buffers, after a
vim file was opened once in the session.
Fix this by defining the autocmd only local to the current buffer.
See also :help autocmd-buflocal
Instead of only sourcing the vim config when vimrc or $MYVIMRC (xdg.vim)
is edited, reload always when saving a vim file.
This is a test. But I think it makes sense since I never edit a vim file
that is not sourced by my config in any way. Thus reloading should be
always appropriate.
