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` example to the build system without depending on ocamlgraph (color wasn't in the build system anyway)
- no relative links to .byte and .asm
- the necessity to type `ocp-build init` the first time
- compilation in emacs is dirty unless you add the following code in your .emac : 

```
(require 'ansi-color)
(defun colorize-compilation-buffer ()
  (toggle-read-only)
  (ansi-color-apply-on-region (point-min) (point-max))
  (toggle-read-only))
(add-hook 'compilation-filter-hook 'colorize-compilation-buffer)
(with-temp-buffer (insert (shell-command-to-string "ocp-edit-mode emacs -load-global-config")) (eval-buffer))
(setq ocp-syntax-coloring t)
```


So, what do you think about switching to ocp-build ?

(I you are agree, don't merge, I must test a bit further)