Add missing `autocmd!`s to `augroup`s

This clears out previous autocommands in that group. That prevents firing the same event repeatedly if I reload my vimrc without restarting Vim.
Add vader.vim plugin

I am using it to test the DetectIndent plugin I am developing
Add more details to NERDTree TODO comments
Add small details to two comments

Update the situation with a TODO to make it easier to continue fixing. And label the code that has no dependencies even though it is in the mappings-with-dependencies section.
Move misplaced comment next to the line it’s about