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 README that explains how to use the rpl_udp example application
Merge pull request #605 from Lotterleben/documentation

added README that explains how to use the rpl_udp example application
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
native readme update
Fixed spelling errors
make buildtest more readable
decolorize buildtest output for jenkins/monochrome
make buildtest fail on error