fix(library/data/list/basic): mark `::` as infixr
fix(frontends/lean/pp): implicit arguments in notation
refactor(frontends/lean/pp): remove 'reverse' hack
fix(frontends/lean/pp): bug in notation matching procedure
feat(frontends/lean/pp): support foldl/foldr notation in the pretty printer
feat(frontends/lean/pp): support foldl/foldr notation in the pretty printer