Merge: Improve ini

Small improvements and fixes for the ini files.

The most important change is how to associate ini file with singleton projects (no dir, only one nit file).
The proposal, from @xymus, is just to add a `.ini` file named like the `.nit`. so `lib/counter.ini` for the project `lib/counter.nit`.

I'm not sure that this feature should be official, consider it just as an easy path to update existing code.

Pull-Request: #1665
Reviewed-by: Alexis Laferrière <alexis.laf@xymus.net>
Reviewed-by: Lucas Bajolet <r4pass@hotmail.com>

diff --cc src/loader.nit
Simple merge