First draft at removing core_kernel dependency

All the stdlib calls has been moved (or are in the process of been moved) to
IrminCore (which might eventually become independant and be used by other
mirage projects).

IrminCore compiles but not the rest of the project.
WIP
Add merlin file
core compiles
More WIP
WIP
More WIP
more WIP
More wip

split Misc into Tc (type-classes) and Misc
Tc can move in a separate library later
More WIP

Separate Hex -- which can go in a separate library -- and Json -- which can go in Ezjsonm.
More WIP
WIP
WIP
More WIP
more WIP ...
More WIP WIP
Add missing autogen files
More WIP.

The MLIs starts to look nice, and the MLs starts to comply with their signatures ...
WIP Ir_commit compiles again
Remove camlp4 from Ir_commit completely