Merge: Relocate examples

Some short programs in `examples` are related to specific libraries. Therefore to improve coupling and cohesion, these examples are moved into a subdirectory of their associated libs.

Basically, it means moving `examples/foo` into `lib/foo/examples`

Pull-Request: #1656
Reviewed-by: Alexis Laferrière <alexis.laf@xymus.net>
Reviewed-by: Lucas Bajolet <r4pass@hotmail.com>

diff --cc lib/mpi/mpi.nit
Simple merge

diff --cc lib/pnacl/pnacl.nit
Simple merge