refactor and clean up native Makefile
valgrind target
added license headers and doxygen file information

plus replaced tabs with spaces
addressed comments from @mehlis
Initial import of low-level driver doxygen groupdef
added LGPL header and doxygen headers
Merge pull request #619 from mehlis/sys-license

added LGPL header and doxygen headers
Merge pull request #606 from OlegHahm/license_issues

added license headers and doxygen file information
added LGPL header and doxygen headers
added LGPL header and doxygen headers
Merge pull request #617 from mehlis/examples-license

added LGPL header and doxygen headers
Merge pull request #601 from LudwigOrtmann/valgrind_target

valgrind target for native
Merge pull request #618 from mehlis/test-license

added LGPL header and doxygen headers
Fixed spelling errors
make buildtest more readable
decolorize buildtest output for jenkins/monochrome
make buildtest fail on error
Do not assume 0x0 to be an unusable address
Merge pull request #611 from haukepetersen/periph_driver_doc

Introduction of a low-level device driver interface
Merge pull request #628 from Kijewski/fno-delete-null-pointer-checks

Do not assume 0x0 to be an unusable address