Simplified and refactored fold.vim (#283)
Simplified and refactored fold.vim (#283)

- Removed g:vimtex_fold_automatic
- Added g:vimtex_fold_manual (currently 1 by default)
- Some simplifications and restructuring

kmarius/vimtex,lervag/vimtex,Aster89/vimtex,kmarius/vimtex,lervag/vimtex,Aster89/vimtex