Merge: Do compilation

refactorization: do in the Compiler classes what was in the ModelBuilder

Just add a method `AbstractCompiler::do_compiling` that contains what the various `ModelBuilder::run_*_compiler` where doing.
This simplifies `separate_erasure_compiler` since most the the code is just inherited.
The specific type handling code is moved into a separate method `compile_types`

Pull-Request: #1065
Reviewed-by: Alexis Laferrière <alexis.laf@xymus.net>

diff --cc src/compiler/separate_erasure_compiler.nit
Simple merge