With ocp build

I made a try to switch our project build manager to ocp-build.

I think it's more up to date with opam. Moreover, there is a nice tool ocp2opam for creation of opam package directly from ocp-build project. The makefile is less complicated. The installation directory is the default used by ocamlfind. 

I split the code in several subfolders to clean up the root directory. 

ocp-build uses separated and threaded compilation and you can easily say what is "library" and what is supposed to be compiled to an executable. 

The drawbacks are the following : 
- lack of documentation for ocp-build
- can't add the "color.ml" in the build system without depending on ocamlgraph (color wasn't in the build system anyway)
- no relative links to .byte and .asm

So, what do you think about switching about switching to ocp-build ?