compiling: moves up the compiling_writer module to be used by the new FFI

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

diff --git a/src/compiling/compiling_writer.nit b/src/compiling_writer.nit
similarity index 100%
rename from src/compiling/compiling_writer.nit
rename to src/compiling_writer.nit