#164983 by multiple contributors: document the core database schemas

modules/aggregator/aggregator.install

modules/block/block.install

modules/book/book.install

modules/comment/comment.install

modules/contact/contact.install

modules/dblog/dblog.install

modules/filter/filter.install

modules/forum/forum.install

modules/locale/locale.install

modules/menu/menu.install

modules/node/node.install

modules/openid/openid.install

modules/poll/poll.install

modules/profile/profile.install

modules/search/search.install

modules/statistics/statistics.install

modules/system/system.install

modules/taxonomy/taxonomy.install

modules/trigger/trigger.install

modules/update/update.install