Build with ocamlbuid

**info**
  - ocamlfind 1.4.1 is required to build the doc. (https://github.com/hhugo/ocaml-findlib/commit/54c52a8993c30af6cfc83bb850f2dbc656cf042a) (we need to wait for a new release)

**directory structure**
```
src
  /syntax
  /ocamlbuild
  /tools
  /lib
    /***.(server | client) .ml (* could be merged into a single eliom file *)
    /server
      /sig
    /client
      /sig
    /common
      /sig
pkg
  /META
  /build.ml (* describe what to build *)
  /filelist.ml (* describe the content the client/server libs *)
  /topkg.ml (* ... *)
  /distillery (* templates *)
  /etc (* ... *)
  /man (* ... *)
build
  /doc.ml (* ocamlbuild and the doc => should be moved in another package *)
  /util.ml (* ocamlbuild and the util  => should be moved in another package *)
  /build.ml (* eliom specific rules, reuse src/ocamlbuild/* *) 
tests
  /distillery
  /testsuite (this one need a huge cleaning)
  /miniwiki
  /monitor (not built: needs updates)
```
**notes** (en vrac)
 - `.eliom` files can be used in `/src/lib` (careful with cyclic deps)
 - no more `./configure` nor `Makefile.config ( need discussion here ! )
 - `tests` need eliom to be installed (was not the case before)
 - `pkg/build.ml` generate `eliom.install` (installation with opam-installer)
 - no more miniforum (highly outdated)

**todo**
  - [x] installation (oasis ? or not ? opam-installer ?) (currently topkg)
  - [x] fix small issue to build the full testsuite
  - [x] check content of client/server libs (*.mllib)
  - [x] check list of documented modules (*.odocl)
  - [ ] update eliom-apiwiki

Please comment and contribute