add mbed_lpc1768 hwtimer stub

closes #586
refactor and clean up native Makefile
valgrind target
added license headers and doxygen file information

plus replaced tabs with spaces
addressed comments from @mehlis
Merge pull request #596 from LudwigOrtmann/mbed_hwtimer_stub

add mbed_lpc1768 hwtimer stub
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
Fix coding conventions in sys/shell/commands/sc_cc2420.c
Fix coding conventions in sys/transceiver/transceiver.c
Allow IEEE 802.15.4 addressing types for transceiver

IEEE 802.15.4 has two addressing modes: 16-bit short and the device's
EUI-64. Currently RIOT supports only sending of packets with 16-bit
short addresses via the transceiver interface. This patch allows at
least for the radio chips that support IEEE 802.15.4 to let the
application/upper layer decide which addressing mode to use.

Upper layer implementation will be implemented in follow-up PR to #460