As_project: make it easier to work with components (type-wise)
Colonless (as in point) change.

Sorry about that but caml-mode renders name: tokens as labels
which makes my interface reading confusing.
As_project reorder things (possibly) logically.
Add .ocp-indent file.
Add available field to project.
Add Assemblage.add for registering projects.

Assemblage.create will now return a project value. This may not be
useful for now but it's just to put us in a good position if we once
want to decide to provide an API to inspect and process project and
component values.
Add Assemblage.{dir,file}.

The first one is to describe directories of build artefacts. The
second one for static files.
Merge pull request #46 from dbuenzli/api-dir-file

API improvements