Merge pull request #3488 from OlegHahm/libcoap_debug_fixes

pkg/libcoap/0001-Add-RIOT-Makefile.patch

pkg/libcoap/0002-Add-config.h.patch

pkg/libcoap/0003-Remove-two-example-programs-in-root.patch

...ap/0004-Eliminate-some-compiler-warnings-and-errors.patch

pkg/libcoap/0005-fix-old-style-function-declarations.patch

pkg/libcoap/0006-debug-do-not-misuse-NDEBUG.patch

pkg/libcoap/0007-fix-option-parsing-with-debug-enabled.patch

pkg/libcoap/0008-fix-debug-out-in-PDU-parsing.patch