Add a few copyright notices
Enhance makefile documentation
Enhance sketch.cpp generation from build/Makefile
Rename CoAP and SPI libraries to included the 'lib' prefix
Fix a small bug in make/system_libs_inc.mk
Enhance libraries/Makefile organisation and documentation
Fix and enhance documentation in libraries/CoAP/src/netinet/ip*
Change Arduino setup() and void() functions into 'extern "C"'
Add stm32/README to briefly explain the source code organisation
WIP: Add libraries/CoAP/src/netinet/net_packet.h and an early test case for it