It demonstrates:
* Adding a module with source code
* Setting a header include directory
* Adding dependences, which are evaluated before other modules dependencies
If the application compiles, everything is ok.
Process `Makefile.include` for external modules. It is included after the others
so it could overwrite some of the configuration if wanted.
Process `Makefile.dep` for external modules. It is included before the others so
it could be parsed before setting 'default' values to dependencies.
