For many modules the `Makefile` contains a line like
```
MODULE:=$(shell basename $(CURDIR))
```
This conclusively shows that we do not have to set the module name
manually.

This PR removes the need to set the module name manually, if it is the
same as the basename. E.g. for `…/sys/vtimer/Makefile` the variable
make `MODULE` will still be `vtimer`, because it is the basename of the
Makefile.

additional:
* exporting include path in sys is mandatory for subfolders
* removed duplicate object file in linker call

* introduced variable for cpu folder

* added some auto dependencies

* fixed some prototypes
* restructured sys