lib/java: fix and improve documentation

Signed-off-by: Alexis Laferrière <alexis.laf@xymus.net>
lib/java: intro `JavaObject::is_java_null`

Signed-off-by: Alexis Laferrière <alexis.laf@xymus.net>
lib/java: use Java's `toString` to implement Nit's `to_s`

Signed-off-by: Alexis Laferrière <alexis.laf@xymus.net>
std: Bug fix in perfect_hashing and delete whitespaces

Signed-off-by: Julien Pagès <julien.projet@gmail.com>
nitvm: Method dispatch is functionnal with perfect hashing

Signed-off-by: Julien Pagès <julien.projet@gmail.com>
Merge: Useful Java services

redef `JavaObject::to_s` and intro `JavaObject::is_java_null` with doc

Pull-Request: #821
Reviewed-by: Lucas Bajolet <r4pass@hotmail.com>
Reviewed-by: Alexandre Terrasa <alexandre@moz-code.org>
Reviewed-by: Jean Privat <jean@pryen.org>
Merge: Method dispatch in nitvm

The method dispatch in the nitvm is now functionnal with perfect hashing.

The dispatch is made by using the virtual table of the class.

Signed-off-by: Julien Pagès <julien.projet@gmail.com>

Pull-Request: #851
Reviewed-by: Jean Privat <jean@pryen.org>
Reviewed-by: Lucas Bajolet <r4pass@hotmail.com>
Reviewed-by: Alexandre Terrasa <alexandre@moz-code.org>