doc: fix doxygen group for cc2538 memory map
doc: add documentation for packet format in mc1322x
doc: order the main modules in a more sensible way
doc: remove superfluous and erroneous @file params
doc: don't use defgroup and addtogroup
doc: cleanup for radio_driver
doc: put rpl_storing header to right doxygen group
doc: add or move module description where missing
tests: make embUnit a normal sys module

There is nothing quite special about embUnit.

This PR makes it a normal sys module, so that you can use it in any
application / test.
embunit: fix outputters for msp430
Merge pull request #2150 from OlegHahm/more_doc_cleanup

doc: More documentation cleanup
Merge pull request #2102 from Kijewski/embunit-module

tests: make embUnit a normal sys module