Add missing base_files to lib component.

Fixes #81.
Add cmi and cmti to lib files, temporary fix.

Fixes #81.
Add Features.native_toolchain.

Fixes #87.
Improve generated makefile readability.

And a bit of the makefile generation code.
Put project specifics of As_makefile in As_project_makefile.

May eventually help fixing #56. This is a first step the module
still depends on As_features and a few ad-hoc things ad to
be exported because As_project_makefile funs were using
*internal* things (Variable.case, and the name raw record
field of Variable).
As_makefile.Variable becomes As_makefile.Var.
As_makefile, remove file name from makefile data structure.
As_makefile.write_file, remove logging.

As_tools should do the logging.
As_makefile no longer depends on As_features.

Could be forked of from the project.
Replace As_makefile.Var.name by As_makefile.Var.ref.

That's what it really is.
Replace As_makefile.Var.raw_name by As_makefile.Var.name.

Since the last commit liberated that name.
Tweaks to generated make help.
Tweak Makefile logging.

Especially don't be yellowish for too long it's unreadable in
certain terminals (namely in the untweaked emacs' one). Also
favour reading the build artefacts it makes it easier to
orientate in case of error. Don't try to align too much, we
run too quickly in the 80th column.
Makefile: make all calls to ocamlfind indirect.

Fixes #89. Drastically improves build peformance in some cases since
we call ocamlfind less (from 17s to 10s on a large example that uses
~15 packages, from 2.9s to 2.5s for assemblage).
Merge pull request #91 from dbuenzli/makefile-split

Makefile changes (generation code and generated)
Remove dependency on ocamlgraph. Dead code only.
As_project: reorder things logically.
As_project: (internal) rename parents to path_to_root.

As it includes the component you apply the fun to.
As_project: rename Component.source to Component.source_dir

This is what it is.
As_project: rename Component.filter to Component.filter_map.

That name is more accurate.