lib: update standard library to latest FFI spec

At this commit, nitg can be compiled using nitg compiled from Nit in
the previous commit.

Signed-off-by: Alexis Laferrière <alexis.laf@xymus.net>
tests: update FFI tests to latest spec

Signed-off-by: Alexis Laferrière <alexis.laf@xymus.net>
lib: update the json module to latest FFI spec

Signed-off-by: Alexis Laferrière <alexis.laf@xymus.net>
lib: update md5 module to latest FFI spec

Signed-off-by: Alexis Laferrière <alexis.laf@xymus.net>
lib: update sqlite3 module to latest FFI spec

Signed-off-by: Alexis Laferrière <alexis.laf@xymus.net>
lib: update curl module to the latest FFI spec

Signed-off-by: Alexis Laferrière <alexis.laf@xymus.net>
lib: update gtk3_4 module to the latest FFI spec

Signed-off-by: Alexis Laferrière <alexis.laf@xymus.net>
lib: update mnit module to the latest FFI spec

Signed-off-by: Alexis Laferrière <alexis.laf@xymus.net>
Signed-off-by: Jean Privat <jean@pryen.org>
lib: update the signal module to the latest FFI spec

Signed-off-by: Alexis Laferrière <alexis.laf@xymus.net>
lib: update the curses module to the latest FFI spec

Signed-off-by: Alexis Laferrière <alexis.laf@xymus.net>
lib: update the socket module to the latest FFI spec

Signed-off-by: Alexis Laferrière <alexis.laf@xymus.net>
lib: update sort_downloads to the latest FFI spec

Signed-off-by: Alexis Laferrière <alexis.laf@xymus.net>
lib: update the callback_monkey example to the latest FFI spec

Signed-off-by: Alexis Laferrière <alexis.laf@xymus.net>
lib: update json module to the latest FFI spec

Signed-off-by: Alexis Laferrière <alexis.laf@xymus.net>
Merge branch 'ffi_libupdate' into merge_ffi
nitg: intro the nitni module

Offers services defining the tailored API used by the FFI.

Signed-off-by: Alexis Laferrière <alexis.laf@xymus.net>
nitg: intro the common_ffi module and support for the C language

Signed-off-by: Alexis Laferrière <alexis.laf@xymus.net>
nitg: intro the compiler_ffi module to support the FFI in nitg

Signed-off-by: Alexis Laferrière <alexis.laf@xymus.net>
nitg-g: support cast between subtypes of Pointer

Signed-off-by: Alexis Laferrière <alexis.laf@xymus.net>
nitg: activate support for the FFI in nitg

Signed-off-by: Alexis Laferrière <alexis.laf@xymus.net>

Conflicts:
	src/abstract_compiler.nit
	src/separate_compiler.nit