various documentation and API tweaks
various documentation and API tweaks

* Rename Database to Revision and allow Revisions to be constructed
  without a fixed list of tables.  Table instances will be created
  implicitly when inserted into for the first time and removed when
  the last row has been removed.

* Provide a single join method which takes a type instead of separate
  leftOuterJoin and innerJoin methods

* Various documentation clarifications

ReadyTalk/revori,ReadyTalk/revori,ReadyTalk/revori