via (https://www.linux.com/learn/tutorials/442438-vim-tips-folding-fun)
- zf#jcreates a fold from the cursor down # lines.
- zf/stringcreates a fold from the cursor to string .
- zjmoves the cursor to the next fold.
- zkmoves the cursor to the previous fold.
- zoopens a fold at the cursor.
- zOopens all folds at the cursor.
- zmincreases the foldlevel by one.
- zMcloses all open folds.
