refactor(library/data/bool): use new style
refactor(logic/core/eq): use sections
refactor(library/logic): remove 'core' subdirectory
chore(library/logic): fix comments
refactor(data/nat/order): use new policy for marking implicit arguments and '!' operator
refactor(data/int/order): use '!' operator
refactor(data/nat/sub): use new policy for marking implicit arguments and '!' operator
refactor(data/list): use '!' operator, and new name convention for declaration names
refactor(data/sum): use sections
feat(emacs/lean-input): add shortcuts for subscripts
refactor(library/data/prod): cleanup
refactor(library/data/num): cleanup