Removed vars from Response as it is not useful.

Variables to templates should be passed in the action, not through the
Response object.
Makefile uses a generic version of Vala.
Soup already display the libsoup and Valum versions.
Added dependencies for source files in Makefile.
Simplified View into an abstract class that carries its variables.

A view carries a hashmap of values for its rendering instead of being
providen in the render method. This prevent the declaration of a hashmap
that would be used by the view.

path and read are not relevant to view engine that are not
file-based, so it's better to abstract view.

Ctpl can handle views from path.
Added a simple 404 if no route was matched by the router.

Uses append_take instead of deprecated append from Soup Message.
Views should render their errors.

A view cannot return null, but has to render its error.
Accidently took one...