File Release Notes and Changelog

Batteries 2.0, the first backwards incompatible stable release of batteries. The biggest change is that all users can do 'open Batteries' instead of needing 'open Batteries_uni' when compiling without threads. The next biggest change is that batteries has 0 dependencies, so the problems with camomile and its data files are gone.

More changes listed here: https://github.com/ocaml-batteries-team/batteries-included/wiki/Interfacechanges12