syntax: simplify class registration.

Some module signature are made explicit in 'defs.ml'. It allows the
definition of the functor Base.Register.
syntax: introduce the method 'call_expr' in the class 'make_module_expr'.

From the point of view of a class writer, the new method's name seems
more meaningful than the old 'mproject'.
syntax: introduce the method 'wrap' in the class 'make_module_expr'.

It wraps 'str_item list' into a 'module_expr' and allows some more
factorization in classes.
Fix in syntax extension: the expression "x < 1" didn't parse.

Move the 'TRY' statement one step over.
syntax: avoid code duplication when using 'Base.tuple'.
Update README
Prefix runtime module with "Deriving_".

The runtime module name is parametrized in class description.
syntax: simplify dependencies between class.

It only concerns the Pickle_class.
syntax: code cleaning in class.

- Defs.generator#{sum,record,variant}: do not receive the full type declaration as argument anymore

- All class:
  - propagate change from Defs.generator
  - order method consistently
  - reindente some code

- Dump_class:
  - use "call_expr" when possible (see methods "dump_int" and "read_int")
  - use "seq_list" instead of "fold_right" in method "nargs"

- Bounded class:
  - do not use ListLabels (for consistency)

- Eq and Typeable classes:
  - remove the "tup" functions (not useful anymore since previous commit)

- Eq class:
  - use "lprefix" and "rprefix" consistently

- Show:
  - avoid 'fprintf' in generated code (method nargs)

- Pickle:
  - introduce clear distinction between pickler and unpickler
  - name some anonymous functions for better lisibility
syntax: suppress warning in code generated by Pickle.
syntax: Defs: suppress unused functions.
FIX: the function to hash variant labels was not exactly the same as the OCaml ones.

This may lead to different collisions.
syntax: Add int32 and int64 to Eq, Typeable and Pickle.
syntax: move 'context' creation into class.
syntax: rename loc into _loc.
Makefile: Build and install with ocamlfind
syntax: add a type-conv compatibiliy mode
syntax: Types -> represent polymorphic variant argument with a list
syntax: Add function Utils.List.split3
Prepare release (README...)