Update CHANGES
Update to latest Ezjsonm and Mirage-tc (unreleased)
Add Irmin.Default to quickly create Irmin store

It takes 2 parameters: a store builder (given by a backend) and the user-defined contents.
Fix the *very* annoying ocamlbuild warning on 4.02

This warning completely breaks my beloved goto-next-error on emacs.
The command-line tool can use Irmin.Default
Start porting the examples